Update starlette requirement from ~=0.31.1 to ~=0.35.1 in /app

Updates the requirements on [starlette](https://github.com/encode/starlette) to permit the latest version.
- [Release notes](https://github.com/encode/starlette/releases)
- [Changelog](https://github.com/encode/starlette/blob/master/docs/release-notes.md)
- [Commits](encode/starlette@0.31.1...0.35.1)

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

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

app/requirements.txt

@@ -1,5 +1,5 @@
 uvicorn~=0.23.2
-starlette~=0.31.1
+starlette~=0.35.1
 aiofiles~=23.2.1
 jinja2~=3.1.2
 requests~=2.31.0