[Robustness test] Fix wrong error message in loadKeyValueOperations

[henrybear327]

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.86%. Comparing base (f07e2ae) to head (b692041).
Report is 2 commits behind head on main.

Additional details and impacted files

see 28 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19610      +/-   ##
==========================================
+ Coverage   68.77%   68.86%   +0.08%     
==========================================
  Files         421      421              
  Lines       35897    35897              
==========================================
+ Hits        24689    24720      +31     
+ Misses       9786     9751      -35     
- Partials     1422     1426       +4     

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[henrybear327]

/retest

[k8s-ci-robot]

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