allow testpypi deployment to pass when file already uploaded (testing only)

Author: orbeckst

.github/workflows/deploy.yml

@@ -119,7 +119,8 @@ jobs:
         uses: pypa/gh-action-pypi-publish@v1.13.0
         with:
           repository-url: https://test.pypi.org/legacy/
-          verbose: true
+          verbose: true         # useful debugging info (eg wrong classifiers)
+          skip-existing: true   # allows repeated testing with same tag
 
   deploy-pypi:
     name: Deploy to PyPI