ci: update the git diff command in the prevent deletion workflow to i…

…mprove accuracy (#14232) (#14259)

.github/workflows/prevent-deletion.yaml

@@ -23,7 +23,7 @@ jobs:
       - name: Find changes
         run: |
           git rev-parse '${{ github.event.pull_request.head.sha }}'
-          if git diff --name-only --diff-filter 'D' HEAD '${{ github.event.pull_request.head.sha }}' | grep -E '^media/.*\.(jpg|png|jpeg|gif)$' >/tmp/changed_files; then
+          if git diff --merge-base --name-only --diff-filter 'D' HEAD '${{ github.event.pull_request.head.sha }}' | grep -E '^media/.*\.(jpg|png|jpeg|gif)$' >/tmp/changed_files; then
             cat /tmp/changed_files
             echo '{"name":"Image Deletion Check","head_sha":"${{ github.event.pull_request.head.sha }}","status":"completed","conclusion":"failure"}' > /tmp/body.json
             jq \