Fix backmerge workflow to use gh CLI for PR creation

.github/workflows/backmerge-release.yml

@@ -57,36 +57,57 @@ jobs:
             echo "Merge conflicts detected"
           fi
 
-      - name: Create Pull Request
+      - name: Create or update Pull Request
         if: steps.check.outputs.changes == 'true' && steps.merge.outputs.merge_success == 'true'
         id: create-pr
-        uses: dotnet/actions-create-pull-request@e8d799aa1f8b17f324f9513832811b0a62f1e0b1
-        with:
-          token: ${{ secrets.GITHUB_TOKEN }}
-          head: backmerge/release-13.2-to-main
-          base: main
-          title: "[Automated] Backmerge release/13.2 to main"
-          labels: area-engineering-systems
-          body: |
-            ## Automated Backmerge
-
-            This PR merges changes from `release/13.2` back into `main`.
-
-            **Commits to merge:** ${{ steps.check.outputs.behind_count }}
-
-            This PR was created automatically to keep `main` up-to-date with release branch changes.
-            Once approved, it will auto-merge.
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          # Check if a PR already exists for this branch
+          EXISTING_PR=$(gh pr list --head backmerge/release-13.2-to-main --base main --json number --jq '.[0].number // empty')
 
-            ---
-            *This PR was generated by the [backmerge-release](${{ github.server_url }}/${{ github.repository }}/actions/workflows/backmerge-release.yml) workflow.*
+          if [ -n "$EXISTING_PR" ]; then
+            echo "PR #$EXISTING_PR already exists, updating it"
+            echo "pull_request_number=$EXISTING_PR" >> $GITHUB_OUTPUT
+          else
+            PR_BODY="## Automated Backmerge
+
+          This PR merges changes from \`release/13.2\` back into \`main\`.
+
+          **Commits to merge:** ${{ steps.check.outputs.behind_count }}
+
+          This PR was created automatically to keep \`main\` up-to-date with release branch changes.
+          Once approved, it will auto-merge.
+
+          ---
+          *This PR was generated by the [backmerge-release](${{ github.server_url }}/${{ github.repository }}/actions/workflows/backmerge-release.yml) workflow.*"
+
+            # Remove leading whitespace from heredoc-style body
+            PR_BODY=$(echo "$PR_BODY" | sed 's/^          //')
+
+            PR_URL=$(gh pr create \
+              --head backmerge/release-13.2-to-main \
+              --base main \
+              --title "[Automated] Backmerge release/13.2 to main" \
+              --body "$PR_BODY" \
+              --assignee joperezr,radical \
+              --label area-engineering-systems)
+
+            PR_NUMBER=$(echo "$PR_URL" | grep -oE '[0-9]+$')
+            if [ -z "$PR_NUMBER" ]; then
+              echo "::error::Failed to extract PR number from: $PR_URL"
+              exit 1
+            fi
+            echo "pull_request_number=$PR_NUMBER" >> $GITHUB_OUTPUT
+            echo "Created PR #$PR_NUMBER"
+          fi
 
-      - name: Add assignees and enable auto-merge
-        if: steps.create-pr.outputs.pull-request-number
+      - name: Enable auto-merge
+        if: steps.create-pr.outputs.pull_request_number
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          gh pr edit ${{ steps.create-pr.outputs.pull-request-number }} --add-assignee joperezr,radical
-          gh pr merge ${{ steps.create-pr.outputs.pull-request-number }} --auto --merge
+          gh pr merge ${{ steps.create-pr.outputs.pull_request_number }} --auto --merge
 
       - name: Create issue for merge conflicts
         if: steps.check.outputs.changes == 'true' && steps.merge.outputs.merge_success == 'false'