Update pillow requirement from ==11.3.* to ==12.1.* (#5768)

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](https://github.com/python-pillow/Pillow/compare/11.3.0...12.1.0)

---
updated-dependencies:
- dependency-name: pillow
  dependency-version: 12.1.0
  dependency-type: direct:production
...

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pyproject.toml

@@ -75,7 +75,7 @@ dependencies = [
   "paypal-checkout-serversdk==1.0.*",
   "PyJWT==2.10.*",
   "phonenumberslite==9.0.*",
-  "Pillow==11.3.*",
+  "Pillow==12.1.*",
   "pretix-plugin-build",
   "protobuf==6.33.*",
   "psycopg2-binary",