Bump pygments from 2.11.2 to 2.15.0 in /tests

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] <[email protected]>

tests/requirements_frozen.txt

@@ -64,7 +64,7 @@ pure-eval==0.2.2
 pyasn1==0.4.8
 pyasn1-modules==0.2.8
 pycparser==2.21
-Pygments==2.11.2
+Pygments==2.15.0
 pyparsing==3.0.7
 python-dateutil==2.8.2
 pytz==2021.3