chore(deps-dev): bump testcontainers.version in /apps/backend (#309)

Bumps `testcontainers.version` from 1.20.4 to 1.21.4.

Updates `org.testcontainers:junit-jupiter` from 1.20.4 to 1.21.4
- [Release notes](https://github.com/testcontainers/testcontainers-java/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-java/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-java@1.20.4...1.21.4)

Updates `org.testcontainers:postgresql` from 1.20.4 to 1.21.4
- [Release notes](https://github.com/testcontainers/testcontainers-java/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-java/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-java@1.20.4...1.21.4)

---
updated-dependencies:
- dependency-name: org.testcontainers:junit-jupiter
  dependency-version: 1.21.4
  dependency-type: direct:development
  update-type: version-update:semver-minor
- dependency-name: org.testcontainers:postgresql
  dependency-version: 1.21.4
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

apps/backend/pom.xml

@@ -28,7 +28,7 @@
 		<junit.jupiter.version>5.11.3</junit.jupiter.version>
 		<junit.platform.version>1.11.3</junit.platform.version>
 		<mockito.version>5.21.0</mockito.version>
-		<testcontainers.version>1.20.4</testcontainers.version>
+		<testcontainers.version>1.21.4</testcontainers.version>
 		<bytebuddy.version>1.14.18</bytebuddy.version>
 			<!-- SonarQube Configuration (Self-hosted) -->
 			<sonar.host.url>https://sonar-r0w40gg48okc00wkc08oowo4.46.62.252.63.sslip.io</sonar.host.url>