Bump pillow from 7.1.2 to 9.3.0 in /docs

Bumps [pillow](https://github.com/python-pillow/Pillow) from 7.1.2 to 9.3.0.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/main/CHANGES.rst)
- [Commits](python-pillow/Pillow@7.1.2...9.3.0)

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

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

docs/requirements.txt

@@ -14,7 +14,7 @@ Pygments==2.6.1
 setuptools==46.1.3
 docutils==0.16
 mock==4.0.2
-pillow==7.1.2
+pillow==9.3.0
 alabaster==0.7.12
 commonmark==0.9.1
 sphinx==3.1.1