Update fastapi requirement from ~=0.115.7 to ~=0.115.8 in /code/function

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@0.115.7...0.115.8)

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

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

Author: dependabot[bot]

code/function/requirements.txt

@@ -4,7 +4,7 @@
 
 # azure-identity~=1.15.0
 azure-functions~=1.21.3
-fastapi~=0.115.7
+fastapi~=0.115.8
 pydantic-settings~=2.7.1
 httpx~=0.28.1
 azure-monitor-opentelemetry-exporter==1.0.0b33