build(deps): bump nbconvert from 6.3.0 to 6.5.1

Bumps [nbconvert](https://github.com/jupyter/nbconvert) from 6.3.0 to 6.5.1.
- [Release notes](https://github.com/jupyter/nbconvert/releases)
- [Commits](jupyter/nbconvert@6.3.0...6.5.1)

---
updated-dependencies:
- dependency-name: nbconvert
  dependency-type: indirect
...

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

Author: dependabot[bot]