tests: fix flaky TestLedgerErrorValidate

[algorandskiy]

Summary

#6190 introduced retry callbacks and the TestLedgerErrorValidate test with its in-memory ledger was not quite ready for receiving such message that is normal/expected for that kind of concurrent test like this with in-memory ledger.

Test Plan

This is a test fix

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.77%. Comparing base (1d93b27) to head (698d244).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6259      +/-   ##
==========================================
+ Coverage   51.76%   51.77%   +0.01%     
==========================================
  Files         644      644              
  Lines       86506    86506              
==========================================
+ Hits        44777    44792      +15     
+ Misses      38852    38842      -10     
+ Partials     2877     2872       -5     

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