fix: update role and add missing label for search

[nschonni]

Why:

pa11y is flagging the missing labeling on the Action example search page. When looking at the element flagged, noticed it was "text" rather than "search" as well

What's being changed:

Add a aria-label since there doesn't appear to be another label element and placeholder values aren't accessible

Check off the following:

• All of the tests are passing.
• I have reviewed my changes in staging.
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

[janiceilene]

@nschonni Thanks so much for opening a PR! I'll get this triaged for review ✨

[github-actions]

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