fix: install python dependencies in venv

Author: badmonster0

.github/workflows/_test.yml

@@ -28,9 +28,6 @@ jobs:
           with:
             python-version: ${{ matrix.python-version }}
             cache: 'pip'
-        - name: Install Python global dependencies
-          run: |
-            pip install maturin pytest
         - uses: actions/cache@v4
           with:
             path: .venv
@@ -41,5 +38,7 @@ jobs:
           run: |
             python -m venv .venv
             source .venv/bin/activate
+            pip install maturin pytest
             maturin develop
-            pytest python/cocoindex/tests
+            cd python
+            pytest cocoindex/tests