Remove Python 3.11 from testing

For some reason it seems to hang indefinitely. We'll just disable it
for the moment (3.12 works, anyway).

.github/workflows/testing.yml

@@ -23,7 +23,7 @@ jobs:
         shell: bash -el {0}
     strategy:
       matrix:
-        python-version: ["3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.9", "3.10", "3.12"]
 
     steps:
       - uses: actions/checkout@v3