tests: fix a race in TestP2PMetainfoExchange

[algorandskiy]

Summary

Fix a race between making connections and propagating peer info into peer store in TestP2PMetainfoExchange

Test Plan

This is a test fix

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.87%. Comparing base (64ae8b0) to head (2f3e4a4).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6336   +/-   ##
=======================================
  Coverage   51.86%   51.87%           
=======================================
  Files         653      653           
  Lines       87547    87547           
=======================================
+ Hits        45408    45411    +3     
- Misses      39264    39265    +1     
+ Partials     2875     2871    -4     

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