build(deps): bump pygments in /docs in the production-dependencies group

Bumps the production-dependencies group in /docs with 1 update: [pygments](https://github.com/pygments/pygments).


Updates `pygments` from 2.20.0 to 2.21.0
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.20.0...2.21.0)

---
updated-dependencies:
- dependency-name: pygments
  dependency-version: 2.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: production-dependencies
...

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

Author: dependabot[bot]

docs/requirements.txt

@@ -1,7 +1,7 @@
 Babel==2.18.0
 Jinja2==3.1.6
 MarkupSafe==3.0.3
-Pygments==2.20.0
+Pygments==2.21.0
 Sphinx==8.2.3
 certifi==2026.7.22
 chardet==7.6.0