"nikola build" failing due do strange "notebook>=4.0.0" dependency issue

I am able to locally build a nikola site with a simple ipynb file. How it fails to build here in GitLab. I used the same .gitlab-ci.yml configuration mentioned in the documentation.

Following is the error at the end of the pipeline run:

 $ nikola build
 Scanning posts.....[2020-06-23T18:13:47Z] ERROR: Nikola: In order to build this site (compile ipynb), you must install the "notebook>=4.0.0" Python package.
 [2020-06-23T18:13:47Z] ERROR: Nikola: Exiting due to missing dependencies.
 ERROR: Job failed: exit code 5

However, if I scroll up, it shows this:

$ pip3 install jupyter
 Collecting jupyter
   Downloading https://files.pythonhosted.org/packages/83/df/0f5dd132200728a86190397e1ea87cd76244e42d39ec5e88efd25b2abd7e/jupyter-1.0.0-py2.py3-none-any.whl
 Requirement already satisfied: notebook in /usr/lib/python3.6/site-packages (from jupyter) (6.0.3)

The notebook version is already 6.0.3 but it fails saying that I must install notebook>=4.0.0

Files attached for reference:
.gitlab-ci.yml Pipeline error: txt file