Update python-app.yml

.github/workflows/python-app.yml

@@ -16,7 +16,7 @@ jobs:
           python -m pip install --upgrade pip setuptools wheel
           pip install -e '.[tests]'
       - name: Install packages needed for CI
-        run: pip install pre-commit
+        run: pip install pre-commit pytest
       - name: Lint all files
         run: pre-commit run --all-files --show-diff-on-failure
       - name: Run tests