clean old builds

.github/workflows/build.yml

@@ -28,6 +28,9 @@ jobs:
         with:
           ref: "builds"
           path: "builds"
+      
+      - name: Clean old builds
+        run: rm $GITHUB_WORKSPACE/builds/*.cs3
 
       - name: Setup JDK 11
         uses: actions/setup-java@v1
@@ -51,5 +54,5 @@ jobs:
           git config --local user.email "actions@github.com"
           git config --local user.name "GitHub Actions"
           git add .
-          git commit -m "Build $GITHUB_SHA" || exit 0   # do not error if nothing to commit
-          git push
+          git commit --amend -m "Build $GITHUB_SHA" || exit 0   # do not error if nothing to commit
+          git push --force