Remove temporary pip downgrade from CI suite

Author: codingjoe

.github/workflows/ci.yml

@@ -98,7 +98,6 @@ jobs:
     - name: Install redis
       if: matrix.os == 'ubuntu-latest'
       run: sudo apt-get install -y redis-server
-    - run: python -m pip install pip~=21.0  # https://github.com/pypa/pip/issues/11133
     - run: python -m pip install .[${{ matrix.extras }}] codecov
     - run: python -m pip install django~=${{ matrix.django-version }}.0
     - run: python -m pytest