fix: check kill signal against 0 (#50029)

[ti-chi-bot]

This is an automated cherry-pick of #50029

What problem does this PR solve?

Issue Number: ref #49643

Problem Summary:

Previously the kill signal was checked against 1, however TiDB uses non-zero values to indicate a kill signal.

What changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test
  • Simple enough change.

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]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[ti-chi-bot]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/check_dev	b0f34b8	link	true	/test check-dev
idc-jenkins-ci-tidb/build	b0f34b8	link	true	/test build
idc-jenkins-ci-tidb/unit-test	b0f34b8	link	true	/test unit-test

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[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick:

1. It must be approved by the approvers firstly.
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