manually install latest pymeshlab

.github/workflows/python-app.yml

@@ -24,6 +24,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install flake8
+        pip3 install git+https://github.com/cnr-isti-vclab/PyMeshLab
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
     - name: Lint with flake8
       run: |