expression: fix 2 unstable test cases

[bb7133]

What problem does this PR solve?

Issue Number: close #29283 for release-5.3 branch.

This is a partial backport of #29276

Problem Summary:

What is changed and how it works?

Check List

Tests

• Unit test

Side effects

• NA

Documentation

• NA

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:

• XuHuaiyu
• wshwsh12

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[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/b92e145c057c2c84dbc6c0cb146957fa0a8f70f1

[XuHuaiyu]

/merge

[ti-chi-bot]

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

Commit hash: e884557

[ti-chi-bot]

@bb7133: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[XuHuaiyu]

/run-unit-test