I've updated the GitHub workflow to check Python formatting.

This change updates the `_test.yml` GitHub workflow to include a step that verifies Python code formatting using `ruff format --check`.

Ruff has also been added to the dependencies installed during the workflow.

Author: google-labs-jules[bot]

.github/workflows/_test.yml

@@ -42,7 +42,7 @@ jobs:
         - name: Install Python toolchains
           run: |
             source .venv/bin/activate
-            pip install maturin pytest mypy
+            pip install maturin pytest mypy ruff
         - name: Python build
           run: |
             source .venv/bin/activate
@@ -54,4 +54,8 @@ jobs:
         - name: Python tests
           run: |
             source .venv/bin/activate
-            pytest python/cocoindex/tests
+            pytest python/cocoindex/tests
+        - name: Check Python formatting
+          run: |
+            source .venv/bin/activate
+            python -m ruff format --check .