Run environment-independent tests in full parallel mode

An increasing amount of tests, especially in Log4j Core 3.x does not depend on the environment with two exceptions:

- they might read values from `PropertiesUtil`,
- they might write logs to `StatusLogger`.

If these are JUnit 5 tests, we can make a separate Maven Surefire executions to run them:

- all in a single JVM (saves JVM startup time),
- using JUnit 5 parallel mode.