Fix some warnings on docs

[michael-hawker]

Fixes #

Docs for Toolkit PR #

What changes to the docs does this PR provide?

PR Checklist

Please check if your PR fulfills the following requirements:

• Correctly picked the right branch to base the change off (master for new features, live for typos/improvements)
• For new pages, used the provided template
• For new features, added an entry in the Table of Contents
• Ran against a spell and grammar checker
• Contains NO breaking changes

Other information

[opbld30]

Docs Build status updates of commit ab1fdd7:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/controls/HeaderedContentControl.md	✅Succeeded	View
docs/controls/HeaderedItemsControl.md	✅Succeeded	View
docs/controls/TextToolbar.md	✅Succeeded	View
docs/controls/datagrid_guidance/editing_inputvalidation.md	✅Succeeded	View
docs/controls/datagrid_guidance/keyboard_navigation_selection.md	✅Succeeded	View
docs/controls/layout/StaggeredLayout.md	✅Succeeded	View
docs/controls/layout/WrapLayout.md	✅Succeeded	View
docs/extensions/NullableBoolMarkup.md	✅Succeeded	View

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

For any questions, please:

• Try searching the docs.microsoft.com contributor guides
• Post your question in the Docs support channel

[nschonni]

Think you figured it out, but you can also autofix the markdownlint issues with markdownlint --fix "**/*.md"

[opbld31]

Docs Build status updates of commit c44e35e:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/animations/AnimationBuilder.md	✅Succeeded	View
docs/animations/AnimationSet.md	✅Succeeded	View
docs/controls/HeaderedContentControl.md	✅Succeeded	View
docs/controls/HeaderedItemsControl.md	✅Succeeded	View
docs/controls/TextToolbar.md	✅Succeeded	View
docs/controls/datagrid_guidance/editing_inputvalidation.md	✅Succeeded	View
docs/controls/datagrid_guidance/group_sort_filter.md	✅Succeeded	View
docs/controls/datagrid_guidance/keyboard_navigation_selection.md	✅Succeeded	View
docs/controls/layout/StaggeredLayout.md	✅Succeeded	View
docs/controls/layout/WrapLayout.md	✅Succeeded	View
docs/extensions/NullableBoolMarkup.md	✅Succeeded	View
docs/extensions/TextBoxExtensions.md	✅Succeeded	View

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

For any questions, please:

• Try searching the docs.microsoft.com contributor guides
• Post your question in the Docs support channel