1a3c25b019
Related to: #8856
Many tests create their own `ThreadPoolTaskScheduler` beans.
Therefore, its default phase might affect the memory and performance.
* Use `phase = SmartLifecycle.DEFAULT_PHASE / 2` for manual
`ThreadPoolTaskScheduler` beans
* Migrate affected tests classes to JUnit 5
* Make some other configuration adjustments for better performance
**Cherry-pick to `6.2.x`**
(cherry picked from commit 39c99c0719)