CI: use 3.12 for black check

.github/workflows/black.yaml

@@ -15,10 +15,10 @@ jobs:
     steps:
     - uses: actions/checkout@v2
 
-    - name: Set up Python 3.9
+    - name: Set up Python 3.12
       uses: actions/setup-python@v2
       with:
-        python-version: 3.9
+        python-version: 3.12
 
     - name: Install black
       run: pip install black