Bump starlette from 0.26.1 to 0.27.0 in /demos/palm/python/docs-agent

Bumps [starlette](https://github.com/encode/starlette) from 0.26.1 to 0.27.0.
- [Release notes](https://github.com/encode/starlette/releases)
- [Changelog](https://github.com/encode/starlette/blob/master/docs/release-notes.md)
- [Commits](encode/starlette@0.26.1...0.27.0)

---
updated-dependencies:
- dependency-name: starlette
  dependency-type: indirect
...

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