Issue #4506: fix CI concurrency grouping for PR and dispatch runs

[rwilliamspbg-ops]

Motivation

Technical Details

Test Plan

Test Result

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.

[ScottTodd]

What sort of testing have you done on this? Please fill out the PR template (or delete parts of it that don't apply)

[rwilliamspbg-ops]

Motivation

Issue #4506 reported that the current concurrency key can cancel unrelated workflow_dispatch runs on main, and can also produce confusing behavior when PR events arrive as opened and labeled in quick succession.

Technical Details

• Updated the concurrency.group expression in both CI workflows.
• The new key uses github.head_ref for PRs so PR events coalesce to one run.
• The fallback uses github.run_id for non-PR events so workflow_dispatch and other runs on main do not cancel each other unexpectedly.

Changed workflows:

• .github/workflows/ci.yml
• .github/workflows/multi_arch_ci.yml

Test Plan

• Verified the modified workflow files with diagnostics in the workspace.

Test Result

• No workflow diagnostics reported for the edited YAML files.

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.