Bump torchaudio from 2.3.0 to 2.9.1

Bumps [torchaudio](https://github.com/pytorch/audio) from 2.3.0 to 2.9.1.
- [Release notes](https://github.com/pytorch/audio/releases)
- [Commits](pytorch/audio@v2.3.0...v2.9.1)

---
updated-dependencies:
- dependency-name: torchaudio
  dependency-version: 2.9.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -16,7 +16,7 @@ pynvml==11.5.0
 pyyaml==6.0.1
 torch==2.3.0
 torchvision==0.18.0
-torchaudio==2.3.0
+torchaudio==2.9.1
 tqdm==4.67.1
 psutil==5.9.8
 pynvml==11.5.0