There is no need to post-process the framework internal BPPs.
Therefore, mark `GatewayProxyInstantiationPostProcessor`, `GlobalChannelInterceptorProcessor`, `IntegrationFlowBeanPostProcessor`
and `BaseIntegrationFlowDefinition.ReplyProducerCleaner` as an `AopInfrastructureBean`.
This way they are not post-processed via AOP `BeanPostProcessor`
* Migrate `org.springframework.integration.aop` tests to JUnit 5
* Fix race condition in the `FluxMessageChannelTests.noMemoryLeakInFluxMessageChannelForVolatilePublishers()`
where `FluxMessageChannel.upstreamSubscriptions` is updated from a different thread
**Auto-cherry-pick to `6.2.x`**
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