Bump pygments from 2.14.0 to 2.15.0 in /doc

Bumps [pygments](https://github.com/pygments/pygments) from 2.14.0 to 2.15.0.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.14.0...2.15.0)

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

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