[BE] Make merge conflict workflow failure case more descriptive (#4876)

Co-authored-by: PaliC <>
Co-authored-by: Ivan Zaitsev <108101595+izaitsevfb@users.noreply.github.com>

.github/workflows/pr-dependencies-check.yml

@@ -159,7 +159,8 @@ jobs:
             for CONFLICT in "${CONFLICTING_COMMITS[@]}"; do
               echo "- $(git show --oneline -s "$CONFLICT")" >> "$GITHUB_STEP_SUMMARY"
             done
-
+            echo "::set-output name=conflicting_commits::${CONFLICTING_COMMITS[*]}"
+            echo "::set-output name=num_conflicting_commits::${#CONFLICTING_COMMITS[*]}"
             {
               echo ""
               echo "---"
@@ -242,6 +243,12 @@ jobs:
       - name: Fail if PR is Not Mergeable
         if: ${{ steps.pr_merge_check.outputs.pr_is_mergeable == '0' }}
         run: |
-          echo "The value --- ${{ steps.pr_merge_check.outputs.pr_is_mergeable }} --- == 0 but should be 1."
-          echo "Failing the job as PR_IS_MERGEABLE is not 0."
+          PR_NUMBER="${{ steps.extract_pr_number.outputs.pr_number }}"
+          CONFLICTING_COMMITS="${{ steps.pr_merge_check.outputs.conflicting_commits }}"
+          NUM_CONFLICTING_COMMITS="${{ steps.pr_merge_check.outputs.num_conflicting_commits }}"
+          echo "PR #$PR_NUMBER is NOT mergeable into main / revertable (if it is already merged) due to $NUM_CONFLICTING_COMMITS conflicting commits which are:"
+          for CONFLICT in $CONFLICTING_COMMITS; do
+            echo "- $(git show --oneline -s "$CONFLICT")"
+          done
+          echo "Please rebase your PR onto main and resolve the conflicts."
           exit 1