Bump pygments from 2.12.0 to 2.15.0 in /requirements

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](https://github.com/pygments/pygments/compare/2.12.0...2.15.0)

---
updated-dependencies:
- dependency-name: pygments
  dependency-type: indirect
...
Signed-off-by: dependabot[bot] <support@github.com>

requirements/checkdocs.txt

@@ -59,7 +59,7 @@ pip-tools==6.8.0
     # via
     #   -r checkdocs.in
     #   pip-sync-faster
-pygments==2.12.0
+pygments==2.15.0
     # via sphinx
 pyparsing==3.0.9
     # via packaging

requirements/docs.txt

@@ -59,7 +59,7 @@ pip-tools==6.8.0
     # via
     #   -r docs.in
     #   pip-sync-faster
-pygments==2.12.0
+pygments==2.15.0
     # via sphinx
 pyparsing==3.0.9
     # via packaging