Bump starlette in /api_endpoints/v1_postcode_lookup

Bumps [starlette](https://github.com/encode/starlette) from 0.26.1 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](Kludex/starlette@0.26.1...0.40.0)

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

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

Author: dependabot[bot]

api_endpoints/v1_postcode_lookup/requirements.txt

@@ -1,5 +1,5 @@
 sentry-sdk[starlette]==1.19.1
-starlette==0.26.1
+starlette==0.40.0
 mangum==0.17.0
 requests==2.31.0
 https://github.com/DemocracyClub/dc_logging/archive/refs/tags/1.0.2.tar.gz