build(deps): update nbsphinx requirement from <=0.9.7,>=0.8.5 to >=0.8.5,<=0.9.8 in /requirements (#21416)

build(deps): update nbsphinx requirement in /requirements

Updates the requirements on [nbsphinx](https://github.com/spatialaudio/nbsphinx) to permit the latest version.
- [Release notes](https://github.com/spatialaudio/nbsphinx/releases)
- [Changelog](https://github.com/spatialaudio/nbsphinx/blob/master/NEWS.rst)
- [Commits](https://github.com/spatialaudio/nbsphinx/compare/0.8.5...0.9.8)

---
updated-dependencies:
- dependency-name: nbsphinx
  dependency-version: 0.9.8
  dependency-type: direct:production
...

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