Workflows: Include workflow run URL in cherry-pick PR comments

[jigangz]

What?

Add a link to the GitHub Actions workflow run in the comments posted by the cherry-pick-wp-release workflow.

Why?

When the cherry-pick workflow comments on a PR (either for a successful cherry-pick or a conflict notification), there is no link back to the workflow run logs. This makes it harder for contributors to debug failures or verify the cherry-pick. See #76575.

How?

For each actions/github-script step that posts a PR comment, this PR:

1. Adds a run_url environment variable using ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
2. Appends a [Workflow run](${runUrl}) link to the comment body

This applies to both the success comment ("Comment on the PR") and the conflict comment ("Comment on the PR about conflict") steps.

Testing Instructions

This change only affects workflow comment formatting. It can be verified by:

1. Triggering the cherry-pick workflow on a test PR with the appropriate label
2. Confirming the resulting comment includes a clickable link to the workflow run

Fixes #76575

[github-actions]

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[github-actions]

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Co-authored-by: jigangz <jigangz@git.wordpress.org>
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[github-actions]

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[jigangz]

Note: this is a reopen of #76577, which was closed unintentionally. I rebased to fix a git author email mismatch (commits were using a local auto-generated email instead of my GitHub-linked one), which accidentally broke the branch history. All changes are the same as the original PR.