remove py 3.9 testing

.github/workflows/build_and_test.yml

@@ -1,4 +1,4 @@
-name: Build and test [Python 3.9, 3.10, 3.11]
+name: Build and test [Python 3.10, 3.11]
 
 on: [push, pull_request]
 
@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.9, "3.10", "3.11"]
+        python-version: ["3.10", "3.11"]
 
     steps:
       - name: Checkout