Goroutine leak when replace stmt exceed mem_quota

[wshwsh12]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

drop table if exists t1, t2, t3;
create table t1 (id int key, a int, index (a));
create table t2 (id int key, a int, index (a), constraint fk_1 foreign key (a) references t1(a));
alter table t2 drop foreign key fk_1;
alter table t2 add constraint fk_1 foreign key (a) references t1(a) on delete set null;
replace into t1 values (1, 1);
set tidb_mem_quota_query = 8500;
replace into t1 values (1, 2);

2. What did you expect to see? (Required)

No goroutine leak.

3. What did you see instead (Required)

goroutine 42087 [semacquire]:
sync.runtime_Semacquire(0xc003a75f4c?)
	/usr/local/go/src/runtime/sema.go:62 +0x25
sync.(*WaitGroup).Wait(0xc0070302a0?)
	/usr/local/go/src/sync/waitgroup.go:116 +0x48
github.com/pingcap/tidb/pkg/store/copr.(*copIteratorTaskSender).run(0xc0030d24b0, 0xc0093ccb70?)
	/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/store/copr/coprocessor.go:912 +0x1d0
created by github.com/pingcap/tidb/pkg/store/copr.(*copIterator).open in goroutine 21407
	/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/store/copr/coprocessor.go:879 +0x405

goroutine 43539 [select]:
github.com/pingcap/tidb/pkg/store/copr.(*copIteratorWorker).sendToRespCh(0xc0065313b0?, 0x63aa108?, 0xc006542f00?, 0x6?)
	/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/store/copr/coprocessor.go:1003 +0xa6
github.com/pingcap/tidb/pkg/store/copr.(*copIteratorWorker).run(0xc0065313b0, {0x63aa108, 0xc006542f00})
	/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/store/copr/coprocessor.go:821 +0xe5
created by github.com/pingcap/tidb/pkg/store/copr.(*copIterator).open in goroutine 21407
	/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/store/copr/coprocessor.go:861 +0x99

goroutine 50402 [select]:
github.com/pingcap/tidb/pkg/store/copr.(*copIteratorWorker).sendToRespCh(0xc00c9435e0?, 0x63aa108?, 0xc00dc74750?, 0x50?)
	/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/store/copr/coprocessor.go:1003 +0xa6
github.com/pingcap/tidb/pkg/store/copr.(*copIteratorWorker).run(0xc00c9435e0, {0x63aa108, 0xc00dc74750})
	/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/store/copr/coprocessor.go:821 +0xe5
created by github.com/pingcap/tidb/pkg/store/copr.(*copIterator).open in goroutine 21407
	/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/store/copr/coprocessor.go:861 +0x99

4. What is your TiDB version? (Required)

ed291b8