ci(black): fix used version

.github/workflows/black.yml

@@ -15,6 +15,5 @@ jobs:
     - uses: actions/checkout@v4
     - uses: actions/setup-python@v5
       with:
-        python-version: 3.9
-    - uses: psf/black@21.8b0
-
+        python-version: '3.x'
+    - uses: psf/black@stable