Only run release workflow on master branch

Author: joschi

.github/workflows/release.yml

@@ -9,7 +9,7 @@ env:
 jobs:
   release:
     runs-on: ubuntu-latest
-    if: github.ref == 'refs/heads/main'
+    if: github.ref == 'refs/heads/master'
     steps:
       - uses: actions/checkout@v2
       - name: Set up JDK 11