chore(deps): bump org.testcontainers:testcontainers-bom in /backend (#328)

Bumps [org.testcontainers:testcontainers-bom](https://github.com/testcontainers/testcontainers-java) from 1.21.3 to 2.0.3.
- [Release notes](https://github.com/testcontainers/testcontainers-java/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-java/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-java@1.21.3...2.0.3)

---
updated-dependencies:
- dependency-name: org.testcontainers:testcontainers-bom
  dependency-version: 2.0.3
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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Author: dependabot[bot]