[fix][test] fix flaky testSplitBundleAdminApi

[heesung-sn]

Fixes #19908

Motivation

Fixes the flaky test.

Modifications

Wrap the assertion statement in the Awaitility loop in case admin.namespaces().getBundles(DEFAULT_NAMESPACE); returns old bundle split state.

Verifying this change

• Make sure that the change passes the CI checks.
  This change is already covered by existing tests.

I tried to run this test in my local fork, heesung-sn#51, with invocation=30.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: heesung-sn#51

[heesung-sn]

@Demogorgon314 Please review this change.

[codecov-commenter]

Codecov Report

Merging #21019 (01a305d) into master (63d9eaf) will increase coverage by 36.22%.
Report is 7 commits behind head on master.
The diff coverage is 100.00%.

@@              Coverage Diff              @@
##             master   #21019       +/-   ##
=============================================
+ Coverage     36.92%   73.14%   +36.22%     
- Complexity    12187    32275    +20088     
=============================================
  Files          1698     1875      +177     
  Lines        129846   139455     +9609     
  Branches      14163    15334     +1171     
=============================================
+ Hits          47947   102011    +54064     
+ Misses        75570    29386    -46184     
- Partials       6329     8058     +1729     

Flag	Coverage Δ
inttests	24.11% <20.00%> (-0.04%)	⬇️
systests	25.08% <20.00%> (-0.07%)	⬇️
unittests	72.45% <100.00%> (+40.36%)	⬆️

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

Files Changed	Coverage Δ
...g/apache/pulsar/client/impl/RawBatchConverter.java	93.50% <100.00%> (+19.82%)	⬆️
...rg/apache/pulsar/compaction/TwoPhaseCompactor.java	74.88% <100.00%> (+4.70%)	⬆️

... and 1436 files with indirect coverage changes