tests: fix TestBuildSplitKeyspaces

[rleungx]

What problem does this PR solve?

Issue Number: ref #9806

What is changed and how does it work?

Check List

Tests

• Unit test

Release note

None.

[ti-chi-bot]

@rleungx: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
non-block/pull-unit-test-next-gen	7a3b683	link	false	/test pull-unit-test-next-gen

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.91%. Comparing base (1d4b63b) to head (7a3b683).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9810      +/-   ##
==========================================
+ Coverage   76.86%   76.91%   +0.04%     
==========================================
  Files         491      491              
  Lines       78311    78311              
==========================================
+ Hits        60197    60230      +33     
+ Misses      14422    14406      -16     
+ Partials     3692     3675      -17     

Flag	Coverage Δ
unittests	76.91% <ø> (+0.04%)	⬆️

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JmPotato, lhy1024

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Needs approval from an approver in each of these files:

• OWNERS [JmPotato,lhy1024]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-10-13 02:43:32.996658635 +0000 UTC m=+62119.073911185: ☑️ agreed by lhy1024.
• 2025-10-13 08:43:39.331613558 +0000 UTC m=+83725.408866118: ☑️ agreed by JmPotato.