ci: use setup.py instead of pip install

.github/workflows/tests.yml

@@ -21,7 +21,7 @@ jobs:
         run: |
           python -m pip install --upgrade pip setuptools wheel
           python -m pip install -r requirements.txt
-          pip install .
+          python setup.py develop
       - name: Run tests
         run: pytest -v --pyargs cyarray --benchmark-save benchmark-stats --benchmark-json benchmark-full.json --benchmark-histogram