testing: Fix a typo in agreement test

[algorandskiy]

Summary

Fix for a strange assert found by JJ

Test Plan

This is a test fix

[jannotti]

Seems right to me.

[codecov-commenter]

Codecov Report

Merging #3651 (2b69cee) into master (cbf1939) will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3651      +/-   ##
==========================================
- Coverage   48.10%   48.05%   -0.05%     
==========================================
  Files         381      381              
  Lines       62080    62080              
==========================================
- Hits        29864    29833      -31     
- Misses      28800    28820      +20     
- Partials     3416     3427      +11     

Impacted Files	Coverage Δ
util/metrics/gauge.go	68.00% <0.00%> (-2.67%)	⬇️
util/metrics/counter.go	78.57% <0.00%> (-2.39%)	⬇️
network/wsPeer.go	68.88% <0.00%> (-2.23%)	⬇️
catchup/peerSelector.go	98.95% <0.00%> (-1.05%)	⬇️
ledger/acctupdates.go	65.46% <0.00%> (-0.95%)	⬇️
data/transactions/verify/txn.go	44.15% <0.00%> (-0.87%)	⬇️
catchup/service.go	69.38% <0.00%> (-0.75%)	⬇️
network/wsNetwork.go	62.79% <0.00%> (-0.50%)	⬇️
ledger/internal/eval.go	71.87% <0.00%> (-0.29%)	⬇️

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