Always align the group headers at the beginning of the line

[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 primer#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: 29dccba

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

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