Add 3.13 also to these runs

Author: Geoff Bache

.github/workflows/self-test.yml

@@ -13,7 +13,7 @@ jobs:
       matrix:
         os: [ubuntu-latest, windows-latest]
         build_env: [native]
-        python: [3.9, '3.10', 3.11, 3.12]
+        python: [3.9, '3.10', 3.11, 3.12, 3.13]
         include:
           - os: windows-latest
             build_env: msys