chore(deps): bump org.junit:junit-bom from 5.13.2 to 6.0.0 in /backend

Bumps [org.junit:junit-bom](https://github.com/junit-team/junit-framework) from 5.13.2 to 6.0.0.
- [Release notes](https://github.com/junit-team/junit-framework/releases)
- [Commits](junit-team/junit-framework@r5.13.2...r6.0.0)

---
updated-dependencies:
- dependency-name: org.junit:junit-bom
  dependency-version: 6.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

backend/build.gradle

@@ -29,7 +29,7 @@ dependencies {
 
 	testCompileOnly 'org.projectlombok:lombok:1.18.38'
 	testAnnotationProcessor 'org.projectlombok:lombok:1.18.38'
-	testImplementation platform('org.junit:junit-bom:5.13.2')
+	testImplementation platform('org.junit:junit-bom:6.0.0')
 	testImplementation 'org.junit.jupiter:junit-jupiter'
 	testImplementation 'io.projectreactor:reactor-test' // Add this for StepVerifier