fix(ci): remove upstream-only workflows after sync-upstream merge

The sync-upstream workflow merges from blockscout/blockscout, which
re-introduces all chain-specific release/publish workflows we deleted.
Those workflows then trigger on release events, causing notification spam.

Added a cleanup step that removes all workflow files except our 3
DOS-specific ones (deploy-config, publish-regular, sync-upstream)
after each upstream merge.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: JOY

.github/workflows/sync-upstream.yml

@@ -134,6 +134,37 @@ jobs:
 
           echo "result=success" >> $GITHUB_OUTPUT
 
+      - name: Remove upstream-only workflows
+        if: steps.target.outputs.skip == 'false' && steps.merge.outputs.result == 'success'
+        run: |
+          # Keep ONLY our DOS-specific workflows, delete everything else
+          KEEP_FILES=(
+            "deploy-config.yml"
+            "publish-regular-docker-image-on-demand.yml"
+            "sync-upstream.yml"
+          )
+
+          cd .github/workflows/
+          for f in *.yml; do
+            KEEP=false
+            for keep in "${KEEP_FILES[@]}"; do
+              if [ "$f" = "$keep" ]; then
+                KEEP=true
+                break
+              fi
+            done
+            if [ "$KEEP" = false ]; then
+              echo "  Removing upstream workflow: $f"
+              rm "$f"
+            fi
+          done
+          cd ../..
+
+          if git diff --name-only | grep -q '\.github/workflows/'; then
+            git add .github/workflows/
+            git commit -m "chore: remove upstream-only workflows after sync"
+          fi
+
       - name: Push and tag
         if: steps.target.outputs.skip == 'false' && steps.merge.outputs.result == 'success'
         run: |