Remove 3.9 testing

Author: rocky

.github/workflows/ubuntu.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ['3.9', '3.10', '3.11', '3.12', '3.13']
+        python-version: ['3.10', '3.11', '3.12', '3.13']
     steps:
     - uses: actions/checkout@v4
     - name: Set up Python ${{ matrix.python-version }}