Fix definition of Python version

Author: hagenw

.github/workflows/test.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macOS-latest, windows-latest]
-        python-version: [3.8, 3.9, 3.10]
+        python-version: ['3.8', '3.9', '3.10']
 
     steps:
     - uses: actions/checkout@v4