parser: restore set_var value to string instead of plain text (#50515)

[ti-chi-bot]

This is an automated cherry-pick of #50515

What problem does this PR solve?

Issue Number: close #50507

Problem Summary: parser: restore set_var value to string instead of plain text

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

[AilinKid]

conflicts

[fixdb]

@qw4990 please fix the conflicts.

[fixdb]

+1

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-02-19 13:54:21.315378731 +0000 UTC m=+278950.063001843: ☑️ agreed by winoros.
• 2024-02-20 04:52:40.045971444 +0000 UTC m=+332848.793594555: ☑️ agreed by fixdb.

[qw4990]

/retest

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-7.5@d686efd). Click here to learn what that means.
The diff coverage is 100.0000%.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #50536   +/-   ##
================================================
  Coverage               ?   72.0083%           
================================================
  Files                  ?       1404           
  Lines                  ?     407771           
  Branches               ?          0           
================================================
  Hits                   ?     293629           
  Misses                 ?      94424           
  Partials               ?      19718           

Flag	Coverage Δ
unit	72.0083% <100.0000%> (?)

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

Components	Coverage Δ
dumpling	53.9913% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.3143% <0.0000%> (?)

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fixdb, tangenta, winoros

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