explaintest: don't use test database in explaintest

[Defined2014]

What problem does this PR solve?

Issue Number: ref #45961

Problem Summary: remove use test in explaintest, avoid environmental problems.

What is changed and how it works?

Check List

Tests

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

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 @Defined2014. Thanks for your PR.

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[codecov]

Codecov Report

Merging #46449 (28538ba) into master (2163271) will decrease coverage by 0.1887%.
Report is 21 commits behind head on master.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #46449        +/-   ##
================================================
- Coverage   73.4346%   73.2460%   -0.1887%     
================================================
  Files          1295       1324        +29     
  Lines        393757     406313     +12556     
================================================
+ Hits         289154     297608      +8454     
- Misses        86235      90277      +4042     
- Partials      18368      18428        +60     

Flag	Coverage Δ
integration	26.1833% <ø> (?)
unit	73.9210% <ø> (+0.4863%)	⬆️

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

Components	Coverage Δ
dumpling	54.0444% <ø> (ø)
parser	85.1859% <ø> (+0.1226%)	⬆️
br	48.1809% <ø> (-4.1262%)	⬇️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, xhebox

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-08-28 08:49:01.75487609 +0000 UTC m=+1744106.303892074: ☑️ agreed by hawkingrei.
• 2023-08-30 03:31:38.444589049 +0000 UTC m=+1897862.993605035: ☑️ agreed by xhebox.