placement: fix alter placement policy cannot update the relative ranges policy (#52254)

[ti-chi-bot]

This is an automated cherry-pick of #52254

What problem does this PR solve?

Issue Number: close #51712 close #52257

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 72.50000% with 22 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.1@fb7dc74). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.1     #55092   +/-   ##
================================================
  Coverage               ?   71.1601%           
================================================
  Files                  ?       1465           
  Lines                  ?     422037           
  Branches               ?          0           
================================================
  Hits                   ?     300322           
  Misses                 ?     101234           
  Partials               ?      20481           

Flag	Coverage Δ
unit	71.1601% <72.5000%> (?)

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

Components	Coverage Δ
dumpling	53.9957% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	41.0693% <0.0000%> (?)

[rleungx]

/test mysql-test

[tiprow]

@rleungx: No presubmit jobs available for pingcap/tidb@release-8.1

In response to this:

/test mysql-test

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[rleungx]

@nolouch @xhebox @zimulala PTAL

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-02 08:24:36.149868892 +0000 UTC m=+77873.368630501: ☑️ agreed by xhebox.
• 2024-08-05 03:05:30.822113395 +0000 UTC m=+234860.689212482: ☑️ agreed by zimulala.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jiyfhust, xhebox, zimulala

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [xhebox,zimulala]
• pkg/ddl/OWNERS [zimulala]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment