Support dynamic labels for multiple variant ActionMenu

[myabc]

Note

This PR was recreated for the OPF fork from #465

What are you trying to accomplish?

Screenshots

Integration

List the issues that this change affects.

Closes primer#3826

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.

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Accessibility

• Fixes axe scan violation - This change fixes an existing axe scan violation.
• No new axe scan violation - This change does not introduce any new axe scan violations.
• New axe violation - This change introduces a new axe scan violation. Please describe why the violation cannot be resolved below.

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: c4f008c

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

This PR includes changesets to release 1 package

Name	Type
@openproject/primer-view-components	Minor

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[Copilot]

Pull request overview

This PR extends Primer::Alpha::ActionMenu dynamic-label behavior to the multiple-select variant, so the invoker button label reflects all currently selected items (including preselected ones). This aligns ActionMenu behavior more closely with other selection components (e.g., SelectPanel) and addresses the linked accessibility issue.

Changes:

• Update ActionMenu custom element logic to compute and render dynamic labels for data-select-variant="multiple".
• Add/adjust system coverage for dynamic labels in both single- and multiple-select ActionMenu previews.
• Add a changeset documenting the user-facing enhancement.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
test/system/alpha/action_menu_test.rb	Renames the single-select dynamic label test and adds a multiple-select dynamic label test (but leaves an older now-contradictory assertion in the file).
app/components/primer/alpha/action_menu/action_menu_element.ts	Updates #setDynamicLabel() to support multi-select by joining checked item labels and calling it after multi-select toggles.
.changeset/sweet-candies-pay.md	Declares a minor release for adding multi-select dynamic label support.