Align group headers in Primer::Alpha::ActionMenu

[HDinger]

What are you trying to accomplish?

Group headers inside ActionMenus should always be left aligned, no matter how the menu itself is positioned.

Screenshots

Before

After

List the issues that this change affects.

Closes #2950

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.

Merge checklist

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

[changeset-bot]

🦋 Changeset detected

Latest commit: 6a43ffa

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	Patch

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[camertron]

Nice thank you! Could you add a changeset?

[HDinger]

Nice thank you! Could you add a changeset?

Hi @camertron

I already added one, don't know why the changeset action still fails 🤷

[camertron]

Oh weird. Thanks!