Add comments to Python versions in Github workflow

Author: abravalheri

.github/workflows/tests.yml

@@ -14,8 +14,8 @@ jobs:
     strategy:
       matrix:
         python:
-        - 3.7
-        - "3.10"
+        - 3.7  # oldest Python supported by PSF
+        - "3.10"  # newest Python that is stable
         platform:
         - ubuntu-latest
         - macos-latest