requirements: update pillow requirement from <9.1.0 to <9.2.0

Updates the requirements on [pillow](https://github.com/python-pillow/Pillow) to permit the latest version.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/main/CHANGES.rst)
- [Commits](python-pillow/Pillow@1.0...9.1.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -11,7 +11,7 @@ modeci_mdf>=0.3.2, <0.3.4
 modelspec<0.2.0
 networkx<2.8
 numpy<1.21.4, >=1.17.0
-pillow<9.1.0
+pillow<9.2.0
 pint<0.18
 toposort<1.8
 torch>=1.8.0, <2.0.0; (platform_machine == 'AMD64' or platform_machine == 'x86_64') and platform_python_implementation == 'CPython' and implementation_name == 'cpython'