Bump fastapi from 0.115.7 to 0.115.11 in /backend

Bumps [fastapi](https://github.com/fastapi/fastapi) from 0.115.7 to 0.115.11.
- [Release notes](https://github.com/fastapi/fastapi/releases)
- [Commits](fastapi/fastapi@0.115.7...0.115.11)

---
updated-dependencies:
- dependency-name: fastapi
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]