Bump pygments from 2.13.0 to 2.15.0 in /docs (#133)

Bumps [pygments](https://github.com/pygments/pygments) from 2.13.0 to 2.15.0.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.13.0...2.15.0)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -4,4 +4,4 @@ mkdocs-exclude==1.0.2
 mkdocs-material==8.3.9
 mkdocs-simple-hooks==0.1.5
 markdown-include==0.7.0
-pygments==2.13.0
+pygments==2.15.0