Lowering ack callback to avoid race condition

[RanVaknin]

Motivation and Context

This PR addresses an intermittent test failure in Http2PingHandlerTest.delayedPingFlushDoesntTerminateConnectionPrematurely(). The test was occasionally failing with a PingFailedException due to timing issues between ping scheduling, and delayed writes. The test verifies that a delayed ping flush doesn't prematurely terminate the connection, but the race condition in the test setup was causing inconsistent results.

Testing

Even though this test failed intermittently in our CI builds, I ran the test locally with @RepeatedTest(1000) before making changes and observed a 100% success rate locally.
While this wont deterministically solve the issue, the change aims to make these failures even more rare by reducing the response time window.

[davidh44]

Just to check, we don't see any failures with schedulingDelayDoesNotCausePingTimeout() and don't need to make a similar change there?

https://github.com/aws/aws-sdk-java-v2/blob/master/http-clients/netty-nio-client/src/test/java/software/amazon/awssdk/http/nio/netty/internal/http2/Http2PingHandlerTest.java#L125schedulingDelayDoesNotCausePingTimeout()

[RanVaknin]

I re-scanned our logs and in the last 10 we saw 9 total failures for Http2PingHandlerTest, all failures only occurred in delayedPingFlushDoesntTerminateConnectionPrematurely. I decided to add a retryable annotation because Iam less confident now in lowering the callback.

[sonarqubecloud]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)

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