planner: fix show stats_bucket couldn't decode index boundary out (#49945)

[ti-chi-bot]

This is an automated cherry-pick of #49945

What problem does this PR solve?

Issue Number: close #49823

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.

planner: fix show stats_bucket couldn't decode index boundary out

[AilinKid]

/test unit-test

[tiprow]

@AilinKid: No presubmit jobs available for pingcap/tidb@release-7.5

In response to this:

/test unit-test

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AilinKid, winoros

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[winoros]

/retest

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-02-01 07:47:22.320622605 +0000 UTC m=+1638083.884920307: ☑️ agreed by AilinKid.
• 2024-02-01 13:10:12.460179755 +0000 UTC m=+1657454.024477460: ☑️ agreed by winoros.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-7.5@20c3e7d). Click here to learn what that means.
The diff coverage is 100.0000%.

❗ Current head 3b45243 differs from pull request most recent head 6b08fc7. Consider uploading reports for the commit 6b08fc7 to get more accurate results

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #49961   +/-   ##
================================================
  Coverage               ?   72.0036%           
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  Files                  ?       1404           
  Lines                  ?     407764           
  Branches               ?          0           
================================================
  Hits                   ?     293605           
  Misses                 ?      94424           
  Partials               ?      19735           

Flag	Coverage Δ
unit	72.0036% <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	53.3104% <0.0000%> (?)

[wuhuizuo]

/hold
wait for merging of #51164

[wuhuizuo]

/unhold