Bump jupyter-server from 2.15.0 to 2.20.0

Bumps [jupyter-server](https://github.com/jupyter-server/jupyter_server) from 2.15.0 to 2.20.0.
- [Release notes](https://github.com/jupyter-server/jupyter_server/releases)
- [Changelog](https://github.com/jupyter-server/jupyter_server/blob/main/CHANGELOG.md)
- [Commits](jupyter-server/jupyter_server@v2.15.0...v2.20.0)

---
updated-dependencies:
- dependency-name: jupyter-server
  dependency-version: 2.20.0
  dependency-type: direct:production
...

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Author: dependabot[bot]