ttl: don't schedule ttl job when EnableTTLJob is off (#40336)

[ti-chi-bot]

This is an automated cherry-pick of #40336

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

What problem does this PR solve?

Issue Number: close #40335

What is changed and how it works?

Don't try to schedule anything if the EnableTTLJob is false.

Check List

Tests

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

Release note

Fix the issue that the ttl job keeps scheduling even when `tidb_ttl_job_enable` is set to 'OFF'

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

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[wuhuizuo]

/hold high priority for trunk branch

[ti-chi-bot]

/unhold

[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	2c056cf	link	true	/test check-dev
idc-jenkins-ci-tidb/unit-test	2c056cf	link	true	/test unit-test
idc-jenkins-ci-tidb/build	2c056cf	link	true	/test build

Full PR test history. Your PR dashboard.

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