update publishing action using latest instructions

https://github.com/marketplace/actions/pypi-publish

Author: dhellmann

.github/workflows/python-publish.yaml

@@ -30,14 +30,14 @@ jobs:
       run: |
         python setup.py sdist bdist_wheel
     - name: Publish distribution to Test PyPI
-      uses: pypa/gh-action-pypi-publish@master
+      uses: pypa/gh-action-pypi-publish@v1.6.4
       with:
         password: ${{ secrets.TEST_PYPI_PASSWORD }}
         repository_url: https://test.pypi.org/legacy/
     - name: Publish distribution to PyPI
       # This condition prevents PRs from being published as part of
       # the test job.
-      if: startsWith(github.ref, 'refs/tags')
-      uses: pypa/gh-action-pypi-publish@master
+      if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags')
+      uses: pypa/gh-action-pypi-publish@v1.6.4
       with:
         password: ${{ secrets.PYPI_PASSWORD }}