test,ddl: fix data race in TestCancel

[YangKeao]

Signed-off-by: YangKeao yangkeao@chunibyo.icu

What problem does this PR solve?

1. Some variables in the test is used concurrently. I used an atomic variable to read/write them to fix the data race
2. The callback struct is also concurrently modified. I add a clone method to copy it explicitly.
   I have also considered other solutions, for example using non-pointer receiver to implement the callback, so it can be copied automatically when passing into the functions. However, as this struct contains a *BaseCallback, it could cause more problem when misused.

Issue Number: close #37757

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• hawkingrei
• xiongjiwei

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[YangKeao]

Oops, there are more data race in this test. I'll fix them all, just wait a minute 😄

[hawkingrei]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 8a8be33

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! [3] CI still failing after this pr merged.
These failed integration tests don't seem to be introduced by the current PR.

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/common-test	🔴 failed 1, success 10, total 11	52 min	Existing failure
idc-jenkins-ci-tidb/integration-ddl-test	🔴 failed 1, success 5, total 6	23 min	Existing failure
idc-jenkins-ci-tidb/integration-common-test	🔴 failed 2, success 15, total 17	9 min 48 sec	Existing failure
idc-jenkins-ci/integration-cdc-test	🟢 all 37 tests passed	32 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	7 min 18 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	5 min 19 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	5 min 10 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	3 min 21 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	2 min 54 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed