fix: cmd error in pipelines

When a command in a pipeline produces an error, only this single command should fail and return an error.

However the currently implemented behavior is that the complete pipeline execution fails, which isn't resembling the behavior from Redis.

mock.go

@@ -113,7 +113,7 @@ func (h redisClientHook) ProcessPipelineHook(_ redis.ProcessPipelineHook) redis.
 				err = h.returnErr
 			}
 			if err != nil {
-				return err
+				cmd.SetErr(err)
 			}
 		}
 		return nil