Quote versions so they don't get truncated

Action error said it couldn't find 3.1 and some googling suggests it
may be yaml parsing, so lets add quotes to all versions to enure they
aren't truncated.

Author: php1ic

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.7, 3.8, 3.9, 3.10]
+        python-version: ['3.7', '3.8', '3.9', '3.10']
 
     steps:
     - uses: actions/checkout@v2