Bump torch from 2.7.0 to 2.9.0

Bumps [torch](https://github.com/pytorch/pytorch) from 2.7.0 to 2.9.0.
- [Release notes](https://github.com/pytorch/pytorch/releases)
- [Changelog](https://github.com/pytorch/pytorch/blob/main/RELEASE.md)
- [Commits](pytorch/pytorch@v2.7.0...v2.9.0)

---
updated-dependencies:
- dependency-name: torch
  dependency-version: 2.9.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -1,5 +1,5 @@
 # Torch dependencies
-torch==2.7.0
+torch==2.9.0
 # Huggingface dependencies
 transformers[sentencepiece]==4.51.3
 hf-xet==1.1.7