Update starlette requirement from <0.37,>=0.36 to >=0.36,<0.49

Updates the requirements on [starlette](https://github.com/Kludex/starlette) to permit the latest version.
- [Release notes](https://github.com/Kludex/starlette/releases)
- [Changelog](https://github.com/Kludex/starlette/blob/main/docs/release-notes.md)
- [Commits](Kludex/starlette@0.36.0...0.48.0)

---
updated-dependencies:
- dependency-name: starlette
  dependency-version: 0.48.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -1,5 +1,5 @@
 httpx>=0.24,<0.28
-starlette>=0.36,<0.37
+starlette>=0.36,<0.49
 pytest
 pytest==8.2.0
 pytest_asyncio==0.23.6