Update publish-to-pypi.yml

Author: kratzky

.github/workflows/publish-to-pypi.yml

@@ -3,6 +3,7 @@ on: push
 jobs:
   build-n-publish:
     name: Build and publish to PyPI
+    if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags')
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@master