tests: fix waitFinishMerge to stablize the merge test (#7052)

close #7051

Make `waitFinishMerge` assert the keyspace list after the merge is finished rather than every time.

Signed-off-by: JmPotato <ghzpotato@gmail.com>

tests/integrations/mcs/tso/keyspace_group_manager_test.go

@@ -648,14 +648,16 @@ func waitFinishMerge(
 	mergeTargetID uint32,
 	keyspaces []uint32,
 ) {
+	var kg *endpoint.KeyspaceGroup
 	testutil.Eventually(re, func() bool {
-		kg := handlersutil.MustLoadKeyspaceGroupByID(re, server, mergeTargetID)
-		re.Equal(mcsutils.DefaultKeyspaceGroupID, kg.ID)
-		for _, keyspaceID := range keyspaces {
-			re.Contains(kg.Keyspaces, keyspaceID)
-		}
+		kg = handlersutil.MustLoadKeyspaceGroupByID(re, server, mergeTargetID)
+		re.Equal(mergeTargetID, kg.ID)
 		return !kg.IsMergeTarget()
 	})
+	// If the merge is finished, the target keyspace group should contain all the keyspaces.
+	for _, keyspaceID := range keyspaces {
+		re.Contains(kg.Keyspaces, keyspaceID)
+	}
 }
 
 func (suite *tsoKeyspaceGroupManagerTestSuite) TestTSOKeyspaceGroupMergeBeforeInitTSO() {

tests/integrations/mcs/tso/proxy_test.go

@@ -317,7 +317,6 @@ func (s *tsoProxyTestSuite) verifyTSOProxy(
 			for j := 0; j < requestsPerClient; j++ {
 				select {
 				case <-ctx.Done():
-					respErr.Store(ctx.Err())
 					s.cleanupGRPCStream(streams, cleanupFuncs, i)
 					return
 				default: