Drop six from our GitHub Actions (#11621)

Drop https://six.readthedocs.io

Author: cclauss

.github/workflows/build.yml

@@ -20,7 +20,7 @@ jobs:
           key: ${{ runner.os }}-pip-${{ hashFiles('requirements.txt') }}
       - name: Install dependencies
         run: |
-          python -m pip install --upgrade pip setuptools six wheel
+          python -m pip install --upgrade pip setuptools wheel
           python -m pip install pytest-cov -r requirements.txt
       - name: Run tests
         # TODO: #8818 Re-enable quantum tests