Bump starlette from 0.37.1 to 0.40.0 in /tests_integrations/starlette

Bumps [starlette](https://github.com/encode/starlette) from 0.37.1 to 0.40.0.
- [Release notes](https://github.com/encode/starlette/releases)
- [Changelog](https://github.com/encode/starlette/blob/master/docs/release-notes.md)
- [Commits](encode/starlette@0.37.1...0.40.0)

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

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

tests_integrations/starlette/requirements.txt

@@ -10,5 +10,5 @@ idna==3.7
     # via anyio
 sniffio==1.3.0
     # via anyio
-starlette==0.37.1
+starlette==0.40.0
     # via -r requirements.in