[fix][test] Flaky SameAuthParamsLookupAutoClusterFailoverTest

[lhotari]

Fixes #24526

Motivation

The SameAuthParamsLookupAutoClusterFailoverTest.testAutoClusterFailover test is flaky. A prior fix (#25388) addressed one root cause (stale Healthy state in findFailoverTo), but the test still times out intermittently at the "Test recover 2 --> 1" step, where Awaitility waits up to 60s for state to reach [Failed, Healthy, Healthy].

Root cause: with checkHealthyIntervalMs(300) and recoverThreshold(5), recovery of index 1 requires 5 successful probe cycles. Each cycle sequentially probes every index up to currentPulsarServiceIndex (so 3 probes per cycle once currentIndex=2). Each probe is bounded by a 3s deadline in SameAuthParamsLookupAutoClusterFailover.probeAvailable(). Under CI load, the accumulated wall time (cycles × probes × per-probe time) can approach or exceed the 60s Awaitility budget — especially if a transient probe failure of index 1 resets the PreRecover counter, forcing another 5 cycles.

Modifications

Reduce checkHealthyIntervalMs from 300ms to 100ms in the test. This tightens the cycle cadence so recovery completes sooner without weakening the threshold-based state machine — the full five-step PreRecover -> Healthy transition is still exercised.

Verifying this change

• Make sure that the change passes the CI checks.

This change is already covered by existing tests, such as SameAuthParamsLookupAutoClusterFailoverTest.testAutoClusterFailover. Verified locally with @Test(invocationCount = 5) (10 runs total across both enabledTls values): 10/10 passes, each invocation consistent at ~16.5s (vs. the flaky runs that previously exceeded the 60s awaitility budget).

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc-not-needed