Bump pygments from 2.14.0 to 2.15.0 in /docs

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](https://github.com/pygments/pygments/compare/2.14.0...2.15.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

docs/requirements.txt

@@ -45,7 +45,7 @@ myst-parser[linkify]==0.18.1
     # via -r requirements.in
 packaging==23.0
     # via sphinx
-pygments==2.14.0
+pygments==2.15.0
     # via
     #   fluent-pygments
     #   sphinx