Migrate log4j-osgi-test to JUnit 5

[AlbaHerrerias]

Hello 👋

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-osgi-test.

Thank you!

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)

[AlbaHerrerias]

We have some questions we would like to ask. We've found that the test suites CoreOsgiTest, JULProviderTest and SLF4JProviderTest are using PaxExam, and the current version does not support JUnit 5. Before attempting an upgrade, we were wondering, does this feature need to be updated? We are missing some context, what is being checked by using this runner? Any help in this regard is greatly appreciated. Thank you!

[github-actions]

Job	Requested goals	Build Tool Version	Build Outcome	Build Scan®
build-macos-latest	clean install	3.9.8	✅
build-ubuntu-latest	clean install	3.9.8	✅
build-windows-latest	clean install	3.9.8	✅

Generated by gradle/develocity-actions

[ppkarwasz]

Before attempting an upgrade, we were wondering, does this feature need to be updated? We are missing some context, what is being checked by using this runner? Any help in this regard is greatly appreciated. Thank you!

Since PAX Exam is basically dormant, it would be better to move those tests to a different framework, but honestly I don't know which. @HannesWell, any suggestions?

Frameworks like Testcontainer for Java or Arquillian are not very OSGi friendly. The "new" osgi-test assumes that the test is already running in an OSGi environment. Maybe we could use something like laeubisoft/osgi-test-framework or the BND Testing Plugin. I will experiment with the latter. We already use BND plugins and they work well. I would like to keep the list of Open Source vendors we rely on minimal.

[ppkarwasz]

@vy, should we move log4j-osgi-test to the Samples repository (which is our integration test repo).