chore: versions should be strings

Author: portswigger-tim

.github/workflows/test-and-lint.yml

@@ -16,10 +16,10 @@ jobs:
         app:
         - ical-simplejson-proxy
         python-version:
-        - 3.7
-        - 3.8
-        - 3.9
-        - 3.10
+        - '3.7'
+        - '3.8'
+        - '3.9'
+        - '3.10'
     steps:
       - uses: actions/checkout@v3
       - name: Set up Python ${{ matrix.python-version }}