testkit,executor: add MustQueryWitnContext API and fix unstable test TestCoprocessorPriority

[tiancaiamao]

What problem does this PR solve?

Issue Number: close #36974

Problem Summary:

What is changed and how it works?

This is a global one and it affect some other place, make the test unstable.

mockstore.WithClientHijacker(func(c tikv.Client) tikv.Client {
		cli.Client = c
		return cli
	})

I modify the test case to use MustXXXWithContext, and use a special ctx, so the ClientHijacker doesn't affect other place.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• hawkingrei
• tangenta

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[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/24f9bf879a85eed584d222b310560a043781b67a

[tangenta]

/merge

[ti-chi-bot]

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

Commit hash: f25818c

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! New failing [1] after this pr merged.
These new failed integration tests seem to be caused by the current PR, please try to fix these new failed integration tests, thanks!

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/integration-common-test	🟥 failed 1, success 16, total 17	15 min	New failing
idc-jenkins-ci-tidb/common-test	🔴 failed 1, success 10, total 11	15 min	Existing failure
idc-jenkins-ci/integration-cdc-test	🟢 all 36 tests passed	35 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	9 min 52 sec	Existing passed
idc-jenkins-ci-tidb/integration-ddl-test	🟢 all 6 tests passed	7 min 10 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	6 min 38 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	5 min 41 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	4 min 0 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	3 min 14 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed