br: wait tiflash replicas ready && fix unstable test (#46301)

[ti-chi-bot]

This is an automated cherry-pick of #46301

What problem does this PR solve?

Issue Number: close #46302

Problem Summary:

1. restore wait tiflash ready need handle partition tables
2. tiflash refresh ticker need 2 seconds to trigger. so make the test sleep 3 seconds.

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

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-6.5@7241e78). Click here to learn what that means.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-6.5     #46342   +/-   ##
================================================
  Coverage               ?   73.6586%           
================================================
  Files                  ?       1084           
  Lines                  ?     348099           
  Branches               ?          0           
================================================
  Hits                   ?     256405           
  Misses                 ?      75233           
  Partials               ?      16461           

[3pointer]

/run-intergration-br-tests

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: BornChanger, YuJuncen

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• OWNERS [YuJuncen]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-08-23 05:53:25.903365647 +0000 UTC m=+1301570.452381631: ☑️ agreed by BornChanger.
• 2023-08-23 07:07:03.262701264 +0000 UTC m=+1305987.811717251: ☑️ agreed by YuJuncen.

[YuJuncen]

/hold for integration tests.

[3pointer]

/run-intergration-br-tests

[3pointer]

/run-intergration-br-tests

[3pointer]

/run-integration-br-tests

[3pointer]

br integration test passed https://ci.pingcap.net/blue/organizations/jenkins/br_ghpr_unit_and_integration_test/detail/br_ghpr_unit_and_integration_test/16145/pipeline/

[3pointer]

/unhold

[3pointer]

/merge

[ti-chi-bot]

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