Action list description test selector

[camertron]

See: #2971 (thanks @sampart!)

What are you trying to accomplish?

Make it possible to set a test_selector on Primer::Alpha::ActionList::Item#description.

Screenshots

Integration

No changes necessary in production.

List the issues that this change affects.

Closes #2970

Risk Assessment

• Low risk the change is small, highly observable, and easily rolled back.
• Medium risk changes that are isolated, reduced in scope or could impact few users. The change will not impact library availability.
• High risk changes are those that could impact customers and SLOs, low or no test coverage, low observability, or slow to rollback.

What approach did you choose and why?

After discussing with @camertron (thank you!) I went for switching from a passthrough slot to a lambda slot, returning a Primer::BaseComponent so that it can be used with with_content as well as with a block.

Accessibility

• No new axe scan violation - This change does not introduce any new axe scan violations.

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Lookbook)
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

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[changeset-bot]

🦋 Changeset detected

Latest commit: 09b20bd

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/view-components	Minor

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[sampart]

Thanks!