Slighty reorganize matrix include: for clarity

Author: EliahKagan

.github/workflows/pythonpackage.yml

@@ -20,14 +20,17 @@ jobs:
         - os-type: windows
           python-version: "3.13"  # FIXME: Fix and enable Python 3.13 on Windows (#1955).
         include:
+        # Defaults, added to all automatically generated jobs.
         - os-ver: latest
+        - experimental: false
+        # Customized jobs.
         - os-type: ubuntu
           python-version: "3.7"
           os-ver: "22.04"
-        - experimental: false
+          experimental: false
         - os-type: windows
           python-version: "3.13"
-          os-ver: latest  # Somehow the fallback (`- os-ver: latest` by itself) no longer covers this.
+          os-ver: latest
           experimental: true
 
       fail-fast: false