build(deps): Bump mkdocs-material from 9.1.17 to 9.1.21 in /docs (#539)

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material)
from 9.1.17 to 9.1.21.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/squidfunk/mkdocs-material/releases">mkdocs-material's
releases</a>.</em></p>
<blockquote>
<h2>mkdocs-material-9.1.21</h2>
<ul>
<li>Fixed MkDocs 1.4 compat issue in social plugin (9.1.20
regression)</li>
</ul>
<h2>mkdocs-material-9.1.20</h2>
<ul>
<li>Updated Sanskrit translations</li>
<li>Fixed deprecation warnings for social plugin</li>
</ul>
<h2>mkdocs-material-9.1.19</h2>
<ul>
<li>Added support for MkDocs 1.5+</li>
<li>Fixed <a
href="https://redirect.github.com/squidfunk/mkdocs-material/issues/5699">#5699</a>:
Improve error reporting in social plugin</li>
</ul>
<h2>mkdocs-material-9.1.18</h2>
<ul>
<li>Updated Danish translations</li>
<li>Added support for installing user requirements in Docker image</li>
<li>Fixed <a
href="https://redirect.github.com/squidfunk/mkdocs-material/issues/5655">#5655</a>:
Search separator with lookbehind breaks highlighting</li>
</ul>
</blockquote>
</details>
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a
href="https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG">mkdocs-material's
changelog</a>.</em></p>
<blockquote>
<p>mkdocs-material-9.1.21+insiders-4.38.1 (2023-08-01)</p>
<ul>
<li>Improved nested serve mode for projects plugin</li>
<li>Improved compat in privacy plugin with third-party plugins</li>
<li>Fixed <a
href="https://redirect.github.com/squidfunk/mkdocs-material/issues/5790">#5790</a>:
Typeset plugin ignores data-toc-label attribute</li>
<li>Fixed <a
href="https://redirect.github.com/squidfunk/mkdocs-material/issues/5778">#5778</a>:
Interplay of privacy plugin with git-revision-date-localized</li>
<li>Fixed <a
href="https://redirect.github.com/squidfunk/mkdocs-material/issues/5773">#5773</a>:
Info plugin erroring when community edition is in beta</li>
</ul>
<p>mkdocs-material-9.1.21+insiders-4.38.0 (2023-07-29)</p>
<ul>
<li>Added projects plugin for building nested projects</li>
<li>Updated privacy plugin to new MkDocs API</li>
</ul>
<p>mkdocs-material-9.1.21+insiders-4.37.1 (2023-07-28)</p>
<ul>
<li>Updated MkDocs to 1.5.1</li>
<li>Fixed deprecation warning in social plugin due to MkDocs
upgrade</li>
<li>Fixed <a
href="https://redirect.github.com/squidfunk/mkdocs-material/issues/5772">#5772</a>:
Privacy plugin fails due to API change in MkDocs</li>
</ul>
<p>mkdocs-material-9.1.21 (2023-07-27)</p>
<ul>
<li>Fixed MkDocs 1.4 compat issue in social plugin (9.1.20
regression)</li>
</ul>
<p>mkdocs-material-9.1.20 (2023-07-27)</p>
<ul>
<li>Fixed deprecation warnings for social plugin</li>
</ul>
<p>mkdocs-material-9.1.19 (2023-07-18)</p>
<ul>
<li>Added support for MkDocs 1.5+</li>
<li>Fixed <a
href="https://redirect.github.com/squidfunk/mkdocs-material/issues/5699">#5699</a>:
Improve error reporting in social plugin</li>
</ul>
<p>mkdocs-material-9.1.18+insiders-4.37.0 (2023-07-07)</p>
<ul>
<li>Added support for overriding social cards settings per page</li>
<li>Added new social card default/only/image layout</li>
<li>Improved resilience of optimize and social plugin</li>
<li>Fixed rendering bugs for pruned navigation items</li>
<li>Fixed jumping of content tabs anchor links when instant loading is
enabled</li>
<li>Fixed <a
href="https://redirect.github.com/squidfunk/mkdocs-material/issues/5676">#5676</a>:
Optimize plugin doesn't check for pngquant</li>
</ul>
<p>mkdocs-material-9.1.18 (2023-07-03)</p>
<ul>
<li>Updated Danish translations</li>
<li>Added support for installing user requirements in Docker image</li>
<li>Fixed <a
href="https://redirect.github.com/squidfunk/mkdocs-material/issues/5655">#5655</a>:
Search separator with lookbehind breaks highlighting</li>
</ul>
<p>mkdocs-material-9.1.17+insiders-4.36.1 (2023-06-23)</p>
<ul>
<li>Fixed <a
href="https://redirect.github.com/squidfunk/mkdocs-material/issues/5618">#5618</a>:
Date comparison breaking for drafts in blog plugin</li>
</ul>
<!-- raw HTML omitted -->
</blockquote>
<p>... (truncated)</p>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/squidfunk/mkdocs-material/commit/98a009b02a8c76cdf46ec4485260730ebb4a127c"><code>98a009b</code></a>
Prepare 9.1.21 release</li>
<li><a
href="https://github.com/squidfunk/mkdocs-material/commit/feef806a2dcc9dd1e73ca262ce52d48f05c2cc16"><code>feef806</code></a>
Bumped MkDocs to 1.5.0 to mitigate error in social plugin</li>
<li><a
href="https://github.com/squidfunk/mkdocs-material/commit/39580db0ac6d7006498c8c253d8e54b0354d23e4"><code>39580db</code></a>
Updated changelog</li>
<li><a
href="https://github.com/squidfunk/mkdocs-material/commit/08ab76fd0596c68bdc6ea0c7f0c1f8124435b40b"><code>08ab76f</code></a>
Prepare 9.1.20 release</li>
<li><a
href="https://github.com/squidfunk/mkdocs-material/commit/068472a6f7a78d7643aedff90884da1df3300082"><code>068472a</code></a>
Documentation</li>
<li><a
href="https://github.com/squidfunk/mkdocs-material/commit/772421d16dc636beb99740b2e682741ccda32249"><code>772421d</code></a>
Merge pull request <a
href="https://redirect.github.com/squidfunk/mkdocs-material/issues/5759">#5759</a>
from kamilkrzyskow/social-patch2</li>
<li><a
href="https://github.com/squidfunk/mkdocs-material/commit/f548d799911fc63699d665c70f76f0c1479ed97b"><code>f548d79</code></a>
Updated social plugin to use <code>theme.custom_dir</code></li>
<li><a
href="https://github.com/squidfunk/mkdocs-material/commit/3e8faa0fdba72454f0297d06c21bbde75baa10a2"><code>3e8faa0</code></a>
Updated dependencies</li>
<li><a
href="https://github.com/squidfunk/mkdocs-material/commit/b72adf300b0ff71a7c41f36c746faf688956c3ea"><code>b72adf3</code></a>
Updated documentation for custom cookies</li>
<li><a
href="https://github.com/squidfunk/mkdocs-material/commit/ea9446e6cb181880eceef8e10fc8e75b76a703b7"><code>ea9446e</code></a>
Merge branch 'master' of github.com:squidfunk/mkdocs-material</li>
<li>Additional commits viewable in <a
href="https://github.com/squidfunk/mkdocs-material/compare/9.1.17...9.1.21">compare
view</a></li>
</ul>
</details>
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docs/requirements.txt

@@ -1,3 +1,3 @@
-mkdocs==1.4.3
+mkdocs==1.5.1
 mkdocs-glightbox==0.3.4
-mkdocs-material==9.1.17
+mkdocs-material==9.1.21