Fix flaky test

Signed-off-by: Bin Shi <binshi.bing@gmail.com>

pkg/tso/keyspace_group_manager_test.go

@@ -197,7 +197,10 @@ func runTestLoadKeyspaceGroupsAssignment(
 			randomGen := rand.New(rand.NewSource(time.Now().UnixNano()))
 			for j := startID; j < endID; j++ {
 				assignToMe := false
-				if randomGen.Intn(100) < probabilityAssignToMe {
+				// Assign the keyspace group to this host/pod with the given probability,
+				// and the keyspace group manager only loads the keyspace groups with id
+				// less than len(mgr.ams).
+				if j < len(mgr.ams) && randomGen.Intn(100) < probabilityAssignToMe {
 					assignToMe = true
 					mux.Lock()
 					idsExpected = append(idsExpected, j)