next-gen: forbid setting tidb_max_dist_task_nodes in user keyspace

[tangenta]

What problem does this PR solve?

Issue Number: ref #61702

Problem Summary:

What changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

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

[tiprow]

Hi @tangenta. Thanks for your PR.

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[codecov]

Codecov Report

❌ Patch coverage is 22.72727% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.8318%. Comparing base (b2bba33) to head (dba36a7).
⚠️ Report is 183 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #62687        +/-   ##
================================================
+ Coverage   72.8752%   74.8318%   +1.9566%     
================================================
  Files          1769       1818        +49     
  Lines        486105     499130     +13025     
================================================
+ Hits         354250     373508     +19258     
+ Misses       110214     102379      -7835     
- Partials      21641      23243      +1602     

Flag	Coverage Δ
integration	48.7293% <20.0000%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.8700% <ø> (ø)
parser	∅ <ø> (∅)
br	62.7614% <ø> (+16.4525%)	⬆️

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[ti-chi-bot]

[FORMAT CHECKER NOTIFICATION]

Notice: To remove the do-not-merge/needs-tests-checked label, please finished the tests then check the finished items in description.

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Tests

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign benjamin2037, benmeadowcroft, hawkingrei for approval. For more information see the Code Review Process.
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Details

Needs approval from an approver in each of these files:

• OWNERS
• pkg/ddl/OWNERS
• pkg/infoschema/OWNERS
• pkg/planner/OWNERS
• pkg/sessionctx/variable/OWNERS

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[ti-chi-bot]

@tangenta: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
non-block/pull-unit-test-next-gen	dba36a7	link	false	/test pull-unit-test-next-gen
non-block/pull-integration-e2e-test-next-gen	dba36a7	link	false	/test pull-integration-e2e-test-next-gen
non-block/pull-mysql-test-next-gen	dba36a7	link	false	/test pull-mysql-test-next-gen
idc-jenkins-ci-tidb/unit-test	dba36a7	link	true	/test unit-test
pull-integration-realcluster-test-next-gen	dba36a7	link	true	/test pull-integration-realcluster-test-next-gen

Full PR test history. Your PR dashboard.

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[D3Hunter]

replaced by #62995