[workflows:tests] restrict Python 3.12 to '3.12.3'

The changes from .3 to .4 seem to cause errors when running flake8

.github/workflows/tests.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.5", "3.6", "3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "pypy3.9"]
+        python-version: ["3.5", "3.6", "3.7", "3.8", "3.9", "3.10", "3.11", "3.12.3", "pypy3.9"]
 
     steps:
     - uses: actions/checkout@v4