sessionctx, executor: fix failure of reading MaxPreparedStmtCount (#39736) | tidb-test=pr/2117

[ti-chi-bot]

This is an automated cherry-pick of #39736

Also, we cherry-pick #40024 to fix unstable TestMaxPreparedStmtCount.

What problem does this PR solve?

Issue Number: close #39735

Problem Summary:

What is changed and how it works?

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:

• qw4990
• winoros

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[xuyifangreeneyes]

/test check-dev

[fixdb]

+1

[xuyifangreeneyes]

/test mysql-test

[hawkingrei]

/merge

[ti-chi-bot]

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

Commit hash: 2c062e8

[ti-chi-bot]

@ti-chi-bot: The following test 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/mysql-test	a706515	link	true	/test mysql-test

Full PR test history. Your PR dashboard.

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