update ci workflow to install py4cast instead of exporting the

PYTHON_PATH var

.github/workflows/tests.yml

@@ -14,8 +14,6 @@ permissions:
 
 jobs:
   tests:
-    env:
-      PYTHONPATH: '.'
     runs-on: ubuntu-latest
 
     steps:
@@ -30,6 +28,7 @@ jobs:
         pip install -r requirements.txt
         pip install -r requirements_lint.txt
         pip install --timeout 1000 pyg-lib==0.4.0 torch-scatter==2.1.2 torch-sparse==0.6.18 torch-cluster==1.6.2 torch-geometric==2.3.1 -f https://data.pyg.org/whl/torch-2.1.2+cpu.html
+        pip install --editable .
 
     - name: Lint
       run: |