operator: When replacing-down-peer, it should not stop at the step of leave-joint-state (#5789)

ref #5568, close #5788

Signed-off-by: HunDunDM <hundundm@gmail.com>

Co-authored-by: Ti Chi Robot <ti-community-prow-bot@tidb.io>

Author: HunDunDM

server/schedule/operator/step.go

@@ -755,7 +755,7 @@ func (dv DemoteVoter) IsFinish(region *core.RegionInfo) bool {
 			log.Warn("obtain unexpected peer", zap.String("expect", dv.String()), zap.Uint64("obtain-learner", peer.GetId()))
 			return false
 		}
-		return region.GetPendingLearner(peer.GetId()) == nil
+		return peer.GetId() == dv.PeerID
 	}
 	return false
 }

server/schedule/operator/step_test.go

@@ -569,5 +569,12 @@ func (suite *operatorStepTestSuite) check(step OpStep, desc string, testCases []
 		err := step.CheckInProgress(suite.cluster, region)
 		testCase.CheckInProgress(err)
 		_ = step.GetCmd(region, true)
+
+		if _, ok := step.(ChangePeerV2Leave); ok {
+			// Ref https://github.com/tikv/pd/issues/5788
+			pendingPeers := region.GetLearners()
+			region = region.Clone(core.WithPendingPeers(pendingPeers))
+			suite.Equal(testCase.IsFinish, step.IsFinish(region))
+		}
 	}
 }