drop Python 3.9 support

Author: nolze

.github/workflows/ci.yaml

@@ -25,7 +25,7 @@ jobs:
       fail-fast: true
       matrix:
         os: ["ubuntu-latest", "macos-latest", "windows-latest"]
-        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@v3
       - name: Set up Python ${{ matrix.python-version }}