ddl: tidb_scatter_region variable supports setting value in both upper/lower case (#57677)

[ti-chi-bot]

This is an automated cherry-pick of #57677

What problem does this PR solve?

Issue Number: close #57669

Problem Summary: variable should accept upper/lower case

What changed and how does it work?

convert value from uppercase to lowercase

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-8.5@aca349f). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #57741   +/-   ##
================================================
  Coverage               ?   57.0156%           
================================================
  Files                  ?       1770           
  Lines                  ?     627224           
  Branches               ?          0           
================================================
  Hits                   ?     357616           
  Misses                 ?     245602           
  Partials               ?      24006           

Flag	Coverage Δ
integration	36.9551% <50.0000%> (?)
unit	72.7413% <100.0000%> (?)

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

Components	Coverage Δ
dumpling	52.9478% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	52.3321% <0.0000%> (?)

[Benjamin2037]

LGTM

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-11-27 02:14:38.947676921 +0000 UTC m=+602666.567331437: ☑️ agreed by Benjamin2037.
• 2024-11-27 03:01:37.990372637 +0000 UTC m=+605485.610027152: ☑️ agreed by lance6716.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Benjamin2037, benmeadowcroft, lance6716

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Needs approval from an approver in each of these files:

• pkg/ddl/OWNERS [Benjamin2037,lance6716]
• pkg/sessionctx/variable/OWNERS [benmeadowcroft]

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[River2000i]

/retest