tests: increase ListPeersForTopic wait time in TestP2PRelay

[algorandskiy]

Summary

TestP2PRelay failures (one, two) indicate netC messages get lost. Most likely it is not enough time for pubsub to establish its mesh so increased wait time to stabilize the test.

Test Plan

This is a test fix

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.15%. Comparing base (b3c7bca) to head (1cb8326).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6056      +/-   ##
==========================================
- Coverage   56.21%   56.15%   -0.06%     
==========================================
  Files         488      488              
  Lines       69432    69432              
==========================================
- Hits        39030    38990      -40     
- Misses      27761    27789      +28     
- Partials     2641     2653      +12     

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