Bump pygments from 2.11.2 to 2.15.0 in /docs (#18)

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

docs/requirements.txt

@@ -8,7 +8,7 @@ imagesize==1.3.0
 Jinja2==3.1.3
 MarkupSafe==2.1.1
 packaging==21.3
-Pygments==2.11.2
+Pygments==2.15.0
 pyparsing==3.0.8
 pytz==2022.1
 requests==2.31.0