Update versions of Python used in testing (#16)

Remove older versions of Python that Git stopped carrying. Replace with
more recent versions.

Co-authored-by: danholdaway <danholdaway@users.noreply.github.com>

.github/workflows/basic_testing.yaml

@@ -48,7 +48,7 @@ jobs:
 
     strategy:
       matrix:
-        python: ["3.7", "3.8", "3.9", "3.10", "3.11"]
+        python: ["3.9", "3.10", "3.11", "3.12", "3.13"]
 
     steps:
       - name: Setup Python