pip(deps): update fastapi requirement in /backend

Updates the requirements on [fastapi](https://github.com/fastapi/fastapi) to permit the latest version.
- [Release notes](https://github.com/fastapi/fastapi/releases)
- [Commits](fastapi/fastapi@0.118.0...0.128.5)

---
updated-dependencies:
- dependency-name: fastapi
  dependency-version: 0.128.5
  dependency-type: direct:production
...

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

Author: dependabot[bot]

backend/pyproject.toml

@@ -6,7 +6,7 @@ authors = ["Your Name <your.email@example.com>"]
 
 [tool.poetry.dependencies]
 python = "^3.9"
-fastapi = "^0.118.0"
+fastapi = "^0.128.5"
 pydantic = "^2.10.5"
 google-cloud-firestore = "^2.3.4"
 google-cloud-functions = "^1.4.0"