Bump pillow from 8.3.2 to 9.0.0 (#1882)

Bumps [pillow](https://github.com/python-pillow/Pillow) from 8.3.2 to 9.0.0.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/main/CHANGES.rst)
- [Commits](python-pillow/Pillow@8.3.2...9.0.0)

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

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requirements_dev.txt

@@ -1,4 +1,4 @@
 PyGithub==1.52
 Jinja2==2.11.3
 Pygments==2.7.4
-pillow==8.3.2
+pillow==9.0.0