Enable `JUnitPlatform` for Spock tests (#4568)
Enable `JUnitPlatform` for Spock tests (#4568)

Since Spock 2 is based on the JUnit platform, Gradle needs to be configured explicitly to discover and run the tests.
Also, since HikariCP 5 requires JDK 11+, we have to switch back to 4.0.3.
rnorth/test-containers,rnorth/test-containers,testcontainers/testcontainers-java,testcontainers/testcontainers-java,testcontainers/testcontainers-java,rnorth/test-containers