Fix python version in GitHub action

Author: amorison

.github/workflows/tox.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ['3.7', '3.8', '3.9', '3.10']
+        py: ['3.7', '3.8', '3.9', '3.10']
 
     steps:
       - uses: actions/checkout@v2
@@ -24,7 +24,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v2
         with:
-          python-version: ${{ matrix.python }}
+          python-version: ${{ matrix.py }}
       - name: Update pip
         run: python -m pip install -U pip
       - name: Install tox-gh