build(deps): bump pygments from 2.13.0 to 2.15.0 in /docs (#412)

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

docs/requirements.txt

@@ -48,7 +48,7 @@ py==1.11.0; python_version >= "3.7" and python_full_version < "3.0.0" or python_
 pycodestyle==2.7.0; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
 pydocstyle==6.1.1; python_version >= "3.6"
 pyflakes==2.3.1; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
-pygments==2.13.0; python_version >= "3.7"
+pygments==2.15.0; python_version >= "3.7"
 pylint==2.13.9; python_full_version >= "3.6.2"
 pyparsing==3.0.9; python_full_version >= "3.6.8" and python_version >= "3.7"
 pytest-asyncio==0.20.1; python_version >= "3.7"