resume task didn't check ddl conflict

[GMHDBJD]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do? If possible, provide a recipe for reproducing the error.
   create database db
create table db.tb1 (id int)
create table db.tb2 (id int)
start-task
alter table db.tb1 add column a int
alter table db.tb2 add column b int

2. What did you expect to see?
   task will raise error when resume

3. What did you see instead?
   when resume task, syncer will run the second ddl

4. Versions of the cluster

   • DM version (run dmctl -V or dm-worker -V or dm-master -V):

     1.0 and 2.0
     

[WangXiangUSTC]

what is the error message when resume? could you please add an example log.

[WangXiangUSTC]

what is the error message when resume? could you please add an example log.

sorry, I made a mistake, ignore it

[csuzhangxc]

and another PR about this issue #741