Remove useless install in workflow files

Author: bgoujaud

.github/workflows/execute_notebook.yaml

@@ -38,7 +38,6 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install -r requirements.txt
-        pip install pytest "pytest-cov<2.6" codecov
     - name: Install PEPit
       run: |
         pip install -e .