Bump pygments from 2.7.4 to 2.15.0

Bumps [pygments](https://github.com/pygments/pygments) from 2.7.4 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/2.7.4...2.15.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -1,5 +1,5 @@
 mkdocs==1.3.0
 mkdocs-material==4.6.3
 mkdocs-minify-plugin==0.2.3
-pygments==2.7.4
+pygments==2.15.0
 pymdown-extensions==7.0