planner/core: add tests for prepare show statements

[tangenta]

What problem does this PR solve?

Issue Number: close #36422

Problem Summary:

The issue has been fixed by #35136.

What is changed and how it works?

This PR adds some test for it.

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

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:

• hawkingrei
• xhebox

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After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

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[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/f66615b4615e8d3ff6a033d0c06d7f8f569c4b69

[hawkingrei]

/merge

[ti-chi-bot]

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

Commit hash: 8320980

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! New failing [2] after this pr merged.
These new failed integration tests seem to be caused by the current PR, please try to fix these new failed integration tests, thanks!

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci/integration-cdc-test	🟥 failed 1, success 35, total 36	28 min	New failing
idc-jenkins-ci-tidb/integration-ddl-test	🟥 failed 1, success 5, total 6	9 min 35 sec	New failing
idc-jenkins-ci-tidb/integration-common-test	🔴 failed 3, success 8, total 11	1 hr 0 min	Existing failure
idc-jenkins-ci-tidb/common-test	🟢 all 12 tests passed	19 min	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	7 min 11 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	6 min 30 sec	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	6 min 15 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	3 min 32 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	3 min 21 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed