Bump notebook from 6.1.5 to 6.4.1 (#402)

Bumps [notebook](https://github.com/jupyter/jupyterhub) from 6.1.5 to 6.4.1.
- [Release notes](https://github.com/jupyter/jupyterhub/releases)
- [Changelog](https://github.com/jupyterhub/jupyterhub/blob/main/CHECKLIST-Release.md)
- [Commits](https://github.com/jupyter/jupyterhub/commits)

---
updated-dependencies:
- dependency-name: notebook
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements-lock.txt

@@ -57,7 +57,7 @@ nbdime==2.1.1             # via jupyter-cache
 nbformat==5.0.8           # via ipywidgets, jupyter-cache, jupyter-sphinx, jupytext, myst-nb, nbclient, nbconvert, nbdime, notebook
 nest-asyncio==1.4.3       # via nbclient
 nodeenv==1.5.0            # via pre-commit
-notebook==6.1.5           # via nbdime, widgetsnbextension
+notebook==6.4.1           # via nbdime, widgetsnbextension
 packaging==20.4           # via bleach, sphinx
 pandocfilters==1.4.3      # via nbconvert
 pexpect==4.8.0            # via ipython