Add testpypi to poetry repositories

Author: sambhav

.github/workflows/pre-release.yml

@@ -26,6 +26,7 @@ jobs:
         run: |
           poetry env use "3.7"
           poetry install
+          poetry config repositories.testpypi https://test.pypi.org/legacy/
 
       - name: Bump version number
         run: poetry version ${{ github.event.release.tag_name }}