TST: Use Python 3.12 stable

Author: pllim

.github/workflows/ci_workflows.yml

@@ -46,7 +46,7 @@ jobs:
             python-version: '3.11'
             toxenv: py311-test-sphinx72-cov-clocale
           - os: ubuntu-latest
-            python-version: '3.12-dev'
+            python-version: '3.12'
             toxenv: py312-test-sphinxdev
 
           # MacOS X - just the stable and dev