Revert "Support for Python 3.12"

This reverts commit 1ced862c08.

.github/workflows/testing.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-20.04  # Downgrade Ubuntu to 20.04 to fix missing Python 3.6
     strategy:
       matrix:
-        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10", "3.11"]
 
     steps:
     - uses: actions/checkout@v2