AcquireTimerJobsRunnable is not awaiting termination of its ExecutorService

[GeorgiPetkov]

Describe the bug AcquireTimerJobsRunnable#run is not awaiting termination of its ExecutorService (only triggering a shutdown).

Expected behavior AcquireTimerJobsRunnable#run should await the termination of its ExecutorService similarly to DefaultAsyncTaskExecutor#shutdown. All other similar runners don't use ExecutorService at all and really "stop" when they are meant to do so. This causes intermittent test failures and application shutdown issues due to still holding connections to the DB when there is still a running task in the executor service.

Additional context Flowable version: 7.0.0.M1, standalone usage. Database: Postgres 14.