Use official jupyter_core

Author: martinRenou

.github/workflows/main.yml

@@ -131,7 +131,6 @@ jobs:
           python -m pip install jupyterlab_pygments==0.1.0 pytest-cov pytest-rereunfailures flake8 ipywidgets matplotlib traitlets
           yarn install --network-timeout 100000
           python -m pip install ".[test]"
-          python -m pip install git+https://github.com/martinRenou/jupyter_core.git@debug
           cd tests/test_template
           pip install .
           cd ../skip_template