test: stablize test_partition_split_on_append

[BubbleCal]

No description provided.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 97.43590% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.88%. Comparing base (d8f9dcb) to head (fa9dbf9).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
rust/lance/src/index/vector/ivf/v2.rs	97.43%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5181      +/-   ##
==========================================
+ Coverage   81.83%   81.88%   +0.05%     
==========================================
  Files         341      341              
  Lines      140682   140767      +85     
  Branches   140682   140767      +85     
==========================================
+ Hits       115122   115267     +145     
+ Misses      21752    21693      -59     
+ Partials     3808     3807       -1     

Flag	Coverage Δ
unittests	81.88% <97.43%> (+0.05%)	⬆️

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[Xuanwo]

Thank you!