_replicaSetEndpointHandleRequest parses an opMsg to determine what command is in it. If the parse fails, it unconditionally produces a DbResponse containing the parse error. However, we should not return an error if the OpMsg has the fire-and-forget bit set. mongod and mongos today handle this case by silently ignoring the error and not responding.

We may just handle this as part of SERVER-81551 if we refactor how the OpMsgRequest parsing works for the ReplicaSetEndpoint.