executor: fix set names with default_collation_for_utf8mb4 vars (#56469)

[ti-chi-bot]

This is an automated cherry-pick of #56469

What problem does this PR solve?

Issue Number: close #56439

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

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Please upload report for BASE (release-8.1@f94feee). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.1     #56496   +/-   ##
================================================
  Coverage               ?   71.1815%           
================================================
  Files                  ?       1466           
  Lines                  ?     423125           
  Branches               ?          0           
================================================
  Hits                   ?     301187           
  Misses                 ?     101445           
  Partials               ?      20493           

Flag	Coverage Δ
unit	71.1815% <66.6666%> (?)

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

Components	Coverage Δ
dumpling	52.9656% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	41.3149% <0.0000%> (?)

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Defined2014, lance6716

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-10-09 04:56:07.837566661 +0000 UTC m=+1021923.257779672: ☑️ agreed by Defined2014.
• 2024-10-09 06:01:22.460055891 +0000 UTC m=+1025837.880268902: ☑️ agreed by lance6716.

[Defined2014]

/retest