Update pylint.yml with discord and pytest dependencies

.github/workflows/pylint.yml

@@ -17,7 +17,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install pylint
+        pip install pylint discord pytest
     - name: Analysing the code with pylint
       run: |
         pylint $(git ls-files '*.py')