ddl: Update integration test of expr index

[JaySon-Huang]

What problem does this PR solve?

Issue Number: ref #9891, ref pingcap/tidb#61133

Problem Summary:

TiDB disable the invalid expression index ((null)) from being created by pingcap/tidb#61135. Update the integration test cases

What is changed and how it works?

ddl: Fix integration test of expr index
TiDB disable the invalid expression index `((null))` from being created by https://github.com/pingcap/tidb/pull/61135. Update the integration test cases

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

None

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[CalvinNeo]

lgtm

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CalvinNeo, kolafish, Lloyd-Pottiger

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #10188.