ci: Add check for unsigned commits in the PR

- Add verify-signed-commits job that runs on PR
  - check-labels and all downstream jobs are skipped
    if signed commmit verifications fails
  - Fetch all commits in the PR via GitHub API
    and check verification status
  - Fail and print the unsigned commit SHAs if any
    unsigned commits are found.

Co-authored-by: Shubhika Garg <shubhika.garg@openairinterface.org>
Signed-off-by: Jaroslava Fiedlerova <jaroslava.fiedlerova@openairinterface.org>

.github/workflows/jenkins-dispatch.yml

@@ -17,7 +17,36 @@ permissions:
   pull-requests: write
 
 jobs:
+  verify-signed-commits:
+    runs-on: ubuntu-24.04
+
+    if: github.event_name == 'pull_request_target'
+
+    steps:
+      - name: Check all commits are signed
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          UNSIGNED=$(gh api repos/${{ github.repository }}/pulls/${{ github.event.pull_request.number }}/commits \
+            --paginate --jq '[.[] | select(.commit.verification.verified == false) | .sha[:7]] | join(", ")')
+
+          if [ -n "$UNSIGNED" ]; then
+            echo -e "$UNSIGNED commits are missing signature"
+            gh pr comment ${{ github.event.pull_request.number }} --repo ${{ github.repository }} --body "$(cat <<EOF
+          **Validation:**
+          The following commit(s) are missing signature:
+
+          $UNSIGNED
+
+          Please use 'git commit -S' to sign your commits.
+          For detailed instructions, refer to the [CONTRIBUTING.md](https://github.com/duranta-project/openairinterface5g/blob/develop/CONTRIBUTING.md) file at the root of this repository or [GitHub Docs](https://docs.github.com/en/authentication/managing-commit-signature-verification/about-commit-signature-verification)
+          EOF
+          )"
+            exit 1
+          fi
+
   check-labels:
+    needs: verify-signed-commits
     runs-on: ubuntu-24.04
 
     if: github.event_name == 'pull_request_target'