Add keyboard-accessible tooltip for truncated ActionList.Description

[liuliu-dev]

Related issue https://github.com/github/accessibility-audits/issues/14802

Changelog

When ActionList.Description is rendered with truncate, the full text was only visible via a native title attribute — which only appears on mouse hover, not keyboard focus (WCAG SC 2.1.1).

This PR adds a Primer <Tooltip> at the ActionList.Item level that shows the full description text on both hover and keyboard focus when the description is actually truncated.

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 73302eb

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

This PR includes changesets to release 1 package

Name	Type
@primer/react	Patch

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Or, apply the integration-tests: skipped manually label to skip these checks.