Use JUnit 5 for Java Modules integration tests

No idea why we weren't, but using JUnit 4 leads to problems with JDK 21
(some classes being detected as tests even though they aren't),
so let's avoid that.

hibernate-integrationtest-java-modules/hibernate-integrationtest-java-modules.gradle

@@ -27,6 +27,6 @@ dependencies {
 }
 
 test {
-	useJUnit()
+	useJUnitPlatform()
 }