Use strings for python-version

Author: bhrutledge

.github/workflows/main.yml

@@ -14,7 +14,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
         with:
-          python-version: 3.8
+          python-version: '3.8'
       - name: Install dependencies
         run: python -m pip install tox
       - name: Run linting
@@ -23,7 +23,7 @@ jobs:
   test:
     strategy:
       matrix:
-        python: [3.6, 3.7, 3.8, 3.9, 3.10]
+        python: ['3.6', '3.7', '3.8', '3.9', '3.10']
         platform: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.platform }}
     steps:
@@ -51,7 +51,7 @@ jobs:
       - uses: actions/setup-python@v2
         with:
           # Mininum supported Python version
-          python-version: 3.6
+          python-version: '3.6'
       - name: Install dependencies
         run: python -m pip install tox
       - name: Build docs
@@ -65,7 +65,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
         with:
-          python-version: 3.8
+          python-version: '3.8'
       - name: Install dependencies
         run: python -m pip install tox
       - name: Release