Bump pygments from 2.19.2 to 2.20.0 in /docs

Bumps [pygments](https://github.com/pygments/pygments) from 2.19.2 to 2.20.0.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.19.2...2.20.0)

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

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

Author: dependabot[bot]

docs/requirements.txt

@@ -78,7 +78,7 @@ pybtex==0.25.1
     #   sphinxcontrib-bibtex
 pybtex-docutils==1.0.3
     # via sphinxcontrib-bibtex
-pygments==2.19.2
+pygments==2.20.0
     # via sphinx
 pyparsing==3.2.5
     # via matplotlib