ci: test only Python 3.9 and 3.15

Author: slhck

.github/workflows/python-package.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
+        python-version: ["3.9", "3.15"]
 
     steps:
     - uses: actions/checkout@v4