Update pylint.yml

.github/workflows/pylint.yml

@@ -9,15 +9,16 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
-    - name: Set up Python 3.9
+    - name: Set up Python 3.8
       uses: actions/setup-python@v2
       with:
-        python-version: 3.9
+        python-version: 3.8
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
         pip install pylint
         pip install cython
+        pip install mpi4py
         pip install -r requirements.txt
     - name: Analysing the code with pylint
       run: |