* fix #2653

* Update src/StackExchange.Redis/ServerEndPoint.cs

Co-authored-by: Philo <philon@microsoft.com>

* release notes

* merge fail

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Co-authored-by: Philo <philon@microsoft.com>

This is a new feature for allowing keepalive commands to be sent every heartbeat regardless of if they're needed for actual keepalives. I've gotten a ping about a network drop that went undetected for ~8 minutes because of usage only in strings. We see this use case not uncommonly, and because of that string type being the only thing used, we don't detect a protocol fault from subsequent string commands.

The symptoms here are partial/unexpected string payloads but ultimately the wrong answers to the wrong query. Given we don't know at what layer this drop happens (this appears to be extremely rare, 1 in quadrillions as far as we know), the best we can currently do is react to it ASAP.

There may be a better way to accomplish what this is after - discussing with Marc soon as we're both online but prepping this PR in case it's best path.