tests: fix TestP2PRelay data race

[algorandskiy]

Summary

Fix for the following data race:

==================
WARNING: DATA RACE
Read at 0x00c0005202b8 by goroutine 737:
  github.com/algorand/go-algorand/network.TestP2PRelay.TestP2PRelay.func3.func7()
      /home/runner/work/go-algorand/go-algorand/network/p2pNetwork_test.go:907 +0xb4
  github.com/algorand/go-algorand/network.ValidateHandleFunc.ValidateHandle()
      /home/runner/work/go-algorand/go-algorand/network/gossipNode.go:237 +0x121
  go:struct { github.com/algorand/go-algorand/network.ValidateHandleFunc }.ValidateHandle()
      <autogenerated>:1 +0x2a

Previous write at 0x00c0005202b8 by goroutine 731:
  github.com/algorand/go-algorand/network.TestP2PRelay.TestP2PRelay.func3.func7()
      /home/runner/work/go-algorand/go-algorand/network/p2pNetwork_test.go:907 +0x16b
  github.com/algorand/go-algorand/network.ValidateHandleFunc.ValidateHandle()
      /home/runner/work/go-algorand/go-algorand/network/gossipNode.go:237 +0x121
  go:struct { github.com/algorand/go-algorand/network.ValidateHandleFunc }.ValidateHandle()
      <autogenerated>:1 +0x2a

Test Plan

Existing tests

[algorandskiy]

Fixed the linter

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.83%. Comparing base (8521387) to head (871611e).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6316      +/-   ##
==========================================
- Coverage   51.84%   51.83%   -0.02%     
==========================================
  Files         652      652              
  Lines       87433    87433              
==========================================
- Hits        45333    45320      -13     
- Misses      39233    39244      +11     
- Partials     2867     2869       +2     

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