Bump org.mockito:mockito-core from 5.14.2 to 5.15.2 in /server

Bumps [org.mockito:mockito-core](https://github.com/mockito/mockito) from 5.14.2 to 5.15.2.
- [Release notes](https://github.com/mockito/mockito/releases)
- [Commits](mockito/mockito@v5.14.2...v5.15.2)

---
updated-dependencies:
- dependency-name: org.mockito:mockito-core
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

server/build.gradle

@@ -61,7 +61,7 @@ dependencies {
 		exclude group: "com.vaadin.external.google", module: "android-json"
 		exclude group: "org.xmlunit", module: "xmlunit-core"
 	}
-	testImplementation "org.mockito:mockito-core:5.14.2"
+	testImplementation "org.mockito:mockito-core:5.15.2"
 	testImplementation "org.mockito:mockito-junit-jupiter:5.14.2"
 
 	testImplementation "org.testcontainers:testcontainers:${test_container_version}"