remove pluggy upgrade

Author: kip-hart

.github/workflows/python_package.yaml

@@ -31,7 +31,6 @@ jobs:
         python -m pip install --upgrade pip
         pip install setuptools wheel
         pip install flake8 pytest==6.2.5 pytest-cov coveralls
-        pip install --upgrade pluggy
     - name: Install package requirements
       run: pip install -r requirements.txt
     - name: Install package