Docs: Add html_safe example to testing->slots section

[tgaff]

What are you trying to accomplish?

I'm trying to make a (small) testing bump in the road easy to resolve.

I ran into an issue where a tested component was rendering the passed slot as plain text. I thought a doc example with html_safe might help others with testing.

    component.tap do |c|
      c.with_buttons { "<div><button>bigger</button><a href='smaller'>smaller</a></div>" }
    end
    render_inline(component)

Results in the following page.find('.some-class').native.inner_html

<div class=\"flex justify-end gap-3 bg-secondary-50 px-6 py-3\">&lt;div&gt;&lt;button&gt;bigger&lt;/button&gt;&lt;a href='smaller'&gt;smaller&lt;/a&gt;&lt;/div&gt;</div>"

What approach did you choose and why?

It's not really worth it to do templating in tests. This seems like an easy compromise.

Anything you want to highlight for special attention from reviewers?

Nah, this is straightforward I think.

[camertron]

Hey @tgaff, thanks for this! Could you add an entry to CHANGELOG.md please?

[tgaff]

@camertron Done.
Sorry for the commit noise here. I originally just made the change via the web-editor but ended up re-basing it to satisfy the linters.