fix: fixed CI with split dependencies

.github/workflows/python-package.yml

@@ -27,6 +27,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+        if [ -f requirements-dev.txt ]; then pip install -r requirements-dev.txt; fi
     - name: Run tests
       run: |
         export PYTHONPATH="${PYTHONPATH}:/robustbase/"