tests: fix TestP2PEnableGossipService_BothDisable

[algorandskiy]

Summary

After merging #6308 the TestP2PEnableGossipService_BothDisable test became unstable because of a race condition between the check in the test and closing connection in CloseWithoutFlush.
Fixed by manually subscribing to Connected notification to make sure connections were made but still no peers due to EnableGossipService=false option.

Test Plan

This is a test fix

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 51.85%. Comparing base (48e45d0) to head (17f3f59).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
network/p2p/p2p.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6320      +/-   ##
==========================================
- Coverage   51.86%   51.85%   -0.02%     
==========================================
  Files         652      652              
  Lines       87437    87442       +5     
==========================================
- Hits        45350    45339      -11     
- Misses      39222    39239      +17     
+ Partials     2865     2864       -1     

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