Bump pygments from 2.11.2 to 2.15.0 in /docs

Bumps [pygments](https://github.com/pygments/pygments) from 2.11.2 to 2.15.0.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.11.2...2.15.0)

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

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

docs/requirements.txt

@@ -8,7 +8,7 @@ mkdocs-material-extensions==1.0.3
 mkdocstrings==0.18.1
 mkdocstrings-python>=0.5.2
 mkdocstrings-python-legacy==0.2.2
-Pygments==2.11.2
+Pygments==2.15.0
 pymdown-extensions==9.3
 pytkdocs==0.16.1
 docutils==0.18.1