Bump tiktoken from 0.7.0 to 0.9.0

Bumps [tiktoken](https://github.com/openai/tiktoken) from 0.7.0 to 0.9.0.
- [Release notes](https://github.com/openai/tiktoken/releases)
- [Changelog](https://github.com/openai/tiktoken/blob/main/CHANGELOG.md)
- [Commits](openai/tiktoken@0.7.0...0.9.0)

---
updated-dependencies:
- dependency-name: tiktoken
  dependency-version: 0.9.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

src/backend/requirements.txt

@@ -275,7 +275,7 @@ sqlalchemy==2.0.36
     # via fastapi-app (pyproject.toml)
 starlette==0.41.3
     # via fastapi
-tiktoken==0.7.0
+tiktoken==0.9.0
     # via opentelemetry-instrumentation-openai
 tqdm==4.67.1
     # via openai