Updated files with 'repo_helper'. (#26)

Co-authored-by: repo-helper[bot] <74742576+repo-helper[bot]@users.noreply.github.com>

Author: repo-helper[bot]

.github/workflows/mypy.yml

@@ -31,7 +31,7 @@ jobs:
           python -VV
           python -m site
           python -m pip install --upgrade pip setuptools wheel
-          python -m pip install tox
+          python -m pip install --upgrade tox virtualenv
 
       - name: "Run mypy"
         run: "python -m tox -e mypy"