Bump org.jetbrains.kotlin:kotlin-test-junit5

Bumps the kotlin group in /backend with 1 update: [org.jetbrains.kotlin:kotlin-test-junit5](https://github.com/JetBrains/kotlin).


Updates `org.jetbrains.kotlin:kotlin-test-junit5` from 2.3.0 to 2.3.20
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.3.0...v2.3.20)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-test-junit5
  dependency-version: 2.3.20
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: kotlin
...

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

Author: dependabot[bot]

backend/gradle/libs.versions.toml

@@ -4,7 +4,7 @@ exposed = "0.61.0"
 firebase = "9.8.0"
 jackson = "2.21.1"
 junitPlatformLauncher = "1.12.2"
-kotlin = "2.3.0"
+kotlin = "2.3.20"
 liquibase = "5.0.1"
 postgres = "42.7.8"
 springboot = "3.5.11"