Fix: Checkout correct reference branch when contributing using forks

[soumeh01]

Changes

• ${{ github.head_ref }} will look for the feature-branch in the target repository, not the contributor’s fork. If the branch doesn’t exist in the target repo, checkout shall fail when contributed from forks. Instead, use the merge ref for the PR, i.e., “base branch ⨉ PR branch merged”
• Updated ignore list of workflows to prevent redundant runs

Checklist

• 🤖 This change is covered by unit tests (if applicable).
• 🤹 Manual testing has been performed (if necessary).
• 🛡️ Security impacts have been considered (if relevant).
• 📖 Documentation updates are complete (if required).
• 🧠 Third-party dependencies and TPIP updated (if required).

[qltysh]

Diff Coverage: Not applicable. There was no coverage data reported for the files in this diff.

Total Coverage: This PR will not change total coverage.

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[jreineckearm]

LGTM, note that I fixed MD032 on #491 . So, can possibly keep enabled.
Let's merge #491 first, then merge here. Should reduce the PR to the yml file changes.

[jreineckearm]

Thanks, LGTM!