testing: fix bug in TestRekeyUpgrade

[tsachiherman]

Summary

This test has a special handling is case the protocol upgrade completes before we can validate that without an upgrade the rekey feature won't work. However, when that does happen, AccountA is already rekeyed, and would require a different handling.

To avoid that while retaining the execution of the test, I've moved the second part to use a different set of accounts.

Test Plan

This is a test

[codecov-commenter]

Codecov Report

Merging #3026 (bc9a9b8) into master (32e131c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3026   +/-   ##
=======================================
  Coverage   43.83%   43.83%           
=======================================
  Files         386      386           
  Lines       86767    86767           
=======================================
  Hits        38032    38032           
  Misses      42720    42720           
  Partials     6015     6015           

Impacted Files	Coverage Δ
util/metrics/gauge.go	68.00% <0.00%> (-2.67%)	⬇️
util/metrics/counter.go	78.57% <0.00%> (-2.39%)	⬇️
catchup/peerSelector.go	98.95% <0.00%> (-1.05%)	⬇️
catchup/service.go	68.57% <0.00%> (-0.78%)	⬇️
ledger/acctupdates.go	67.21% <0.00%> (-0.10%)	⬇️
network/wsPeer.go	74.35% <0.00%> (+0.51%)	⬆️
data/transactions/verify/txn.go	44.29% <0.00%> (+0.87%)	⬆️
data/abi/abi_type.go	91.81% <0.00%> (+0.90%)	⬆️
ledger/catchpointwriter.go	69.48% <0.00%> (+1.29%)	⬆️
cmd/algoh/blockWatcher.go	80.95% <0.00%> (+3.17%)	⬆️

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[algonautshant]

LGTM