Update pillow requirement from ~=12.1.1 to ~=12.2.0 in /backend

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@12.1.1...12.2.0)

---
updated-dependencies:
- dependency-name: pillow
  dependency-version: 12.2.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -1,3 +1,3 @@
 fastapi~=0.135.1
-pillow~=12.1.1
+pillow~=12.2.0
 uvicorn~=0.44.0