build(deps): bump fastapi from 0.120.4 to 0.121.1 in /backend

Bumps [fastapi](https://github.com/fastapi/fastapi) from 0.120.4 to 0.121.1.
- [Release notes](https://github.com/fastapi/fastapi/releases)
- [Commits](fastapi/fastapi@0.120.4...0.121.1)

---
updated-dependencies:
- dependency-name: fastapi
  dependency-version: 0.121.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]