ActionMenu falsy value bugfix

[joshfarrant]

Summary

Removes check for truthiness in handleItemSelection in ActionMenu.tsx to allow falsy values to trigger item selection callback.

List of notable changes:

• ActionMenu.tsx: Removed check for truthiness in handleItemSelection to allow falsy values to trigger item selection callback.
• ActionMenu.test.tsx: Added a test to assert that falsy items can be selected

Steps to test:

1. Open the ActionMenu Docs
2. Edit the first example to set one of the values to ""
3. Open the ActionMenu and click on the item associated with that value
4. Observe that the onSelect callback is called and triggers an alert.

Supporting resources (related issues, external links, etc):

• 🔗 Link to docs
• Closes 🐛 [BUG] - ActionMenu ignores items whose value is falsy #906

Contributor checklist:

• All new and existing CI checks pass
• Tests prove that the feature works and covers both happy and unhappy paths
• Any drop in coverage, breaking changes or regressions have been documented above
• UI Changes contain new visual snapshots (generated by adding update snapshots label to the PR)
• All developer debugging and non-functional logging has been removed
• Related issues have been referenced in the PR description

Reviewer checklist:

• Check that pull request and proposed changes adhere to our contribution guidelines and code of conduct
• Check that tests prove the feature works and covers both happy and unhappy paths
• Check that there aren't other open Pull Requests for the same update/change

[changeset-bot]

🦋 Changeset detected

Latest commit: 80828fa

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

This PR includes changesets to release 6 packages

Name	Type
@primer/react-brand	Patch
@primer/brand-primitives	Patch
@primer/brand-e2e	Patch
@primer/brand-fonts	Patch
@primer/brand-config	Patch
@primer/brand-storybook	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

🟢 No design token changes found

[github-actions]

🟢 No visual differences found

Our visual comparison tests did not find any differences in the UI.