github CI: test on py312 (w/o -dev)

.github/workflows/ci.yml

@@ -65,7 +65,7 @@ jobs:
               python-version: '3.11'
               toxenv: py311-fuse2
             - os: ubuntu-22.04
-              python-version: '3.12-dev'
+              python-version: '3.12'
               toxenv: py312-fuse3
             - os: macos-12
               python-version: '3.8'