Bump the development-dependencies group in /backend with 3 updates

Bumps the development-dependencies group in /backend with 3 updates: [@types/express](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/express), [eslint](https://github.com/eslint/eslint) and [typescript-eslint](https://github.com/typescript-eslint/typescript-eslint/tree/HEAD/packages/typescript-eslint).


Updates `@types/express` from 4.17.21 to 5.0.0
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/express)

Updates `eslint` from 9.14.0 to 9.15.0
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/main/CHANGELOG.md)
- [Commits](eslint/eslint@v9.14.0...v9.15.0)

Updates `typescript-eslint` from 8.14.0 to 8.15.0
- [Release notes](https://github.com/typescript-eslint/typescript-eslint/releases)
- [Changelog](https://github.com/typescript-eslint/typescript-eslint/blob/main/packages/typescript-eslint/CHANGELOG.md)
- [Commits](https://github.com/typescript-eslint/typescript-eslint/commits/v8.15.0/packages/typescript-eslint)

---
updated-dependencies:
- dependency-name: "@types/express"
  dependency-type: direct:development
  update-type: version-update:semver-major
  dependency-group: development-dependencies
- dependency-name: eslint
  dependency-type: direct:development
  update-type: version-update:semver-minor
  dependency-group: development-dependencies
- dependency-name: typescript-eslint
  dependency-type: direct:development
  update-type: version-update:semver-minor
  dependency-group: development-dependencies
...

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