CI: Add 3.12 to the stable test matrix

Author: effigies

.github/workflows/stable.yml

@@ -105,7 +105,7 @@ jobs:
     strategy:
       matrix:
         os: ['ubuntu-latest', 'windows-latest', 'macos-latest']
-        python-version: [3.8, 3.9, "3.10", "3.11"]
+        python-version: [3.8, 3.9, "3.10", "3.11", "3.12"]
         architecture: ['x64', 'x86']
         install: ['pip']
         check: ['test']