Bump notebook from 6.1.5 to 6.4.1 in /examples/research_projects/lxmert (#13226)

Bumps [notebook](http://jupyter.org) from 6.1.5 to 6.4.1.

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

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

examples/research_projects/lxmert/requirements.txt

@@ -46,7 +46,7 @@ nbclient==0.5.0
 nbconvert==6.0.1
 nbformat==5.0.7
 nest-asyncio==1.4.0
-notebook==6.1.5
+notebook==6.4.1
 numpy==1.19.2
 opencv-python==4.4.0.42
 packaging==20.3