Fix flaky test: test pubsub shardchannels_true #4925

[hank95179]

This PR fixes the flaky test test pubsub shardchannels_true tracked in #4925.

The test was consistently failing with a TimeoutError in CI environments under high load. This indicates that the pubsubShardChannels command sometimes takes longer than the default client timeout to respond, likely due to transient server load or network congestion, causing the test to fail prematurely.

Changes

• Implemented a polling retry mechanism with error handling.
• Wrapped the pubsubShardChannels call in a try-catch block within a retry loop.
• If the command times out or fails transiently, the test now catches the error and retries (up to a limit), making it robust against transient performance dips and network timeouts.

Verification

• Verified locally that the test passes consistently with the added retry logic, even when simulating high load conditions that previously triggered timeouts.

Related Issue

Fixes #4925