Fix that would allow use JDK 21+ to build the project

[robsunday]

Build failed on JDK 21 because JfrContextStorageTest.testAttachLifecycle test failed.
It was caused by the following sequence of actions performed on test start:

1. Mockito’s inline mock maker retransforms ContextAttached.
2. Java 21’s JFR machinery detects that it is an Event subclass and retransforms it again.
3. JFR replaces begin(), commit(), and shouldCommit() with its own implementations. OpenJDK explicitly generates these methods during JFR instrumentation.
4. Mockito’s interception of shouldCommit() is consequently lost.
5. The real method returns false, so this expression effectively becomes: when(false).thenReturn(true) . Since Mockito recorded no invocation, it throws MissingMethodInvocationException.

With this PR Mockito can mock JFR events.

[robsunday]

The inherited final JFR methods satisfy the interface in production, while Mockito can mock the interface without competing with JFR bytecode instrumentation.