Bump pygments from 2.7.4 to 2.15.0 in /docs

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](pygments/pygments@2.7.4...2.15.0)

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

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

docs/notebook_requirements.txt

@@ -39,7 +39,7 @@ prometheus-client==0.3.0
 prompt-toolkit==3.0.30
 ptyprocess==0.6.0
 pycparser==2.20
-Pygments==2.7.4
+Pygments==2.15.0
 pyzmq==22.2.1
 qtconsole==4.3.1
 Send2Trash==1.8.0