Update GitHub Actions workflow to use string format for Python versions

.github/workflows/test.yml

@@ -10,7 +10,7 @@ jobs:
       - name: Set up Python
         uses: actions/[email protected]
         with:
-          python-version: 3.8
+          python-version: "3.8"
       - name: Install dependencies
         run: make install-test
       - name: Lint
@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.8, 3.9, 3.10, 3.11, 3.12, 3.13]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
     steps:
     - uses: actions/checkout@v2
     - name: Set up Python ${{ matrix.python-version }}