Migrate log4j-api-test to junit5

[Realtin]

We are from Neighbourhoodie, the implementation partner of the STF Bug Resilience Program. This work is part of our agreed Milestone 1. Upgrade from JUnit 4 to JUnit 5.
This PR migrates the tests located in log4j-api-test to JUnit5.

Checklist

• Base your changes on 2.x branch if you are targeting Log4j 2; use main otherwise
• ./mvnw verify succeeds (if it fails due to code formatting issues reported by Spotless, simply run ./mvnw spotless:apply and retry)
• Non-trivial changes contain an entry file in the src/changelog/.2.x.x directory
• Tests for the changes are provided
• Commits are signed (optional, but highly recommended)

[Realtin]

Hi @vy I ran into a problem after refactoring the SecurityManagerRule to an Extension. It seems to end up in a loop at: LoaderUtilSecurityManagerTest$TestSecurityManager.checkPermission(LoaderUtilSecurityManagerTest.java:36)
and ends with an error:

org.apache.maven.surefire.booter.SurefireBooterForkException: ExecutionException Error occurred in starting fork, check output in log
[ERROR]         at org.apache.maven.plugin.surefire.booterclient.ForkStarter.awaitResultsDone(ForkStarter.java:456) .... 

Do you have any pointers on how to solve this?

[ppkarwasz]

@Realtin,

I'll look into it tomorrow.