*: fix changefeed checkpoint lag negative value error (#3013)

[ti-chi-bot]

This is an automated cherry-pick of #3013

What problem does this PR solve?

Close #3010

What is changed and how it works?

Check List

Tests

• Manual test (add detailed scripts or steps below)
• Unit test

Code changes

• Has exported function/method change
• Has exported variable/fields change

Side effects

• Possible performance regression
• Increased code complexity

Related changes

• Need to cherry-pick to the release branch

Release note

fix changefeed checkpoint lag negative value error

[ti-chi-bot]

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[asddongmen]

/run-all-tests

[asddongmen]

/run-integration-tests

[amyangfei]

/merge

[ti-chi-bot]

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

Commit hash: 75a2373