expression: fix default value of GetDefaultCollationForUTF8MB4 of StaticExprContext

[lcwangchao]

What problem does this PR solve?

Issue Number: close #53390

What changed and how does it work?

fix default value of GetDefaultCollationForUTF8MB4 of StaticExprContext

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 @lcwangchao. Thanks for your PR.

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[YangKeao]

LGTM

[windtalker]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: windtalker, YangKeao

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-20 07:51:21.817176279 +0000 UTC m=+2071635.574311846: ☑️ agreed by YangKeao.
• 2024-05-20 07:51:58.538017482 +0000 UTC m=+2071672.295153055: ☑️ agreed by windtalker.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.6305%. Comparing base (397a460) to head (310a3b3).
Report is 2 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #53391        +/-   ##
================================================
+ Coverage   72.5545%   74.6305%   +2.0760%     
================================================
  Files          1505       1505                
  Lines        429830     429985       +155     
================================================
+ Hits         311861     320900      +9039     
+ Misses        98694      89195      -9499     
- Partials      19275      19890       +615     

Flag	Coverage Δ
integration	49.4041% <100.0000%> (?)
unit	71.3440% <100.0000%> (-0.1024%)	⬇️

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

Components	Coverage Δ
dumpling	53.9957% <ø> (ø)
parser	∅ <ø> (∅)
br	50.4028% <ø> (+8.9988%)	⬆️