Add black-format checking to CI.

.github/workflows/check-black.yaml

@@ -0,0 +1,14 @@
+name: Check Black formatting
+
+on: [push, pull_request]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: psf/black@stable
+        with:
+            options: "--check --verbose --line-length=120"
+            src: "./pytheneum"
+            version: "~= 24.0"