update pip for ubuntu-bionic

Author: mhils

.github/workflows/ci.yml

@@ -68,6 +68,8 @@ jobs:
     name: "${{ matrix.TEST.TOXENV }} on ${{ matrix.TEST.CONTAINER }}"
     steps:
       - uses: actions/checkout@v2
+      - run: python3 -m pip install -U pip
+        if: 'matrix.TEST.CONTAINER == "ubuntu-bionic"'
       - run: tox -v
         env:
           TOXENV: ${{ matrix.TEST.TOXENV }}