Bump pygments from 2.12.0 to 2.15.0 in /doc/manual

Bumps [pygments](https://github.com/pygments/pygments) from 2.12.0 to 2.15.0.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.12.0...2.15.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

doc/manual/requirements.txt

@@ -16,7 +16,7 @@ packaging==21.3
 pybtex==0.24.0
 pybtex-docutils==1.0.2
 pydata-sphinx-theme==0.8.1
-Pygments==2.12.0
+Pygments==2.15.0
 pyparsing==3.0.9
 pytz==2022.1
 PyYAML==6.0