chore(deps): bump sentence-transformers from 3.2.0 to 3.3.1 in /backend

Bumps [sentence-transformers](https://github.com/UKPLab/sentence-transformers) from 3.2.0 to 3.3.1.
- [Release notes](https://github.com/UKPLab/sentence-transformers/releases)
- [Commits](https://github.com/UKPLab/sentence-transformers/compare/v3.2.0...v3.3.1)

---
updated-dependencies:
- dependency-name: sentence-transformers
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

backend/requirements.txt

@@ -48,7 +48,7 @@ pymilvus==2.4.9
 qdrant-client~=1.12.0
 opensearch-py==2.7.1
 
-sentence-transformers==3.2.0
+sentence-transformers==3.3.1
 colbert-ai==0.2.21
 einops==0.8.0