Try fixing GitHub Actions to use the correct Python

Author: mgorny

.github/workflows/ci.yml

@@ -6,14 +6,16 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["pypy3", "3.6", "3.7", "3.8", "3.9"]
+        python-version: ["3.x", "pypy3", "3.6", "3.7", "3.8", "3.9"]
     steps:
       - name: Check out repository
         uses: actions/checkout@v2
       - name: Install Python
         uses: actions/setup-python@v2
         with:
           python-version: ${{ matrix.python_version }}
+      - name: wtf
+        run: python --version
       - name: Install dependencies
         run: python -m pip install tox
       - name: Run tests