Install pillow in lint pipeline

Author: charlotrudel

.github/workflows/pylint.yml

@@ -29,7 +29,7 @@ jobs:
         if: steps.changed-files.outputs.any_changed == 'true'
         run: |
           sudo apt-get update
-          sudo apt-get install -y python3-tk
+          sudo apt-get install -y python3-tk pillow
           python -m pip install --upgrade pip
           pip install pylint
           python -m pip install mypy