install xgboost which is used in the unit tests of DoubleML

Author: MalteKurz

.github/workflows/pytest.yml

@@ -45,7 +45,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        python -m pip install pytest
+        python -m pip install pytest xgboost
         pip install -r requirements.txt
         pip install .
     - name: Test with pytest