ci: remove pip upgrade

Author: jayvynl

.github/workflows/base-test.yml

@@ -30,7 +30,6 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
-        python -m pip install --upgrade pip
         python -m pip install tox coveralls<3
     - name: Lint code
       run: tox -e lint