Bump the pip group across 1 directory with 2 updates

Bumps the pip group with 2 updates in the /backend directory: [python-multipart](https://github.com/Kludex/python-multipart) and [pymongo](https://github.com/mongodb/mongo-python-driver).


Updates `python-multipart` from 0.0.6 to 0.0.18
- [Release notes](https://github.com/Kludex/python-multipart/releases)
- [Changelog](https://github.com/Kludex/python-multipart/blob/master/CHANGELOG.md)
- [Commits](Kludex/python-multipart@0.0.6...0.0.18)

Updates `pymongo` from 4.3.3 to 4.6.3
- [Release notes](https://github.com/mongodb/mongo-python-driver/releases)
- [Changelog](https://github.com/mongodb/mongo-python-driver/blob/master/doc/changelog.rst)
- [Commits](mongodb/mongo-python-driver@4.3.3...4.6.3)

---
updated-dependencies:
- dependency-name: python-multipart
  dependency-version: 0.0.18
  dependency-type: direct:production
  dependency-group: pip
- dependency-name: pymongo
  dependency-version: 4.6.3
  dependency-type: direct:production
  dependency-group: pip
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -51,12 +51,12 @@ pyasn1==0.6.1
 pycparser==2.22
 pydantic==2.4.2
 pydantic_core==2.10.1
-pymongo==4.3.3
+pymongo==4.6.3
 pyparsing==3.2.3
 python-dateutil==2.9.0.post0
 python-dotenv==1.0.0
 python-jose==3.3.0
-python-multipart==0.0.6
+python-multipart==0.0.18
 pytz==2025.2
 PyYAML==6.0.2
 regex==2024.11.6