Bump ui5-middleware-simpleproxy in /app/travel_processor (#721)

Bumps [ui5-middleware-simpleproxy](https://github.com/ui5-community/ui5-ecosystem-showcase/tree/HEAD/packages/ui5-middleware-simpleproxy) from 3.0.0 to 3.1.1.
- [Changelog](https://github.com/ui5-community/ui5-ecosystem-showcase/blob/main/packages/ui5-middleware-simpleproxy/CHANGELOG.md)
- [Commits](https://github.com/ui5-community/ui5-ecosystem-showcase/commits/ui5-middleware-simpleproxy@3.1.1/packages/ui5-middleware-simpleproxy)

---
updated-dependencies:
- dependency-name: ui5-middleware-simpleproxy
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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