bitswap/network: fix read/write data race in bitswap network test

[gammazero]

connListener events my be written and read at the same time by separate goroutines.

Fix this by using a channel to wait for the writ event to finish before trying to read.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.58%. Comparing base (e69f67e) to head (8c9fa67).
⚠️ Report is 1 commits behind head on main.

@@            Coverage Diff             @@
##             main    #1030      +/-   ##
==========================================
- Coverage   60.59%   60.58%   -0.02%     
==========================================
  Files         268      268              
  Lines       33616    33616              
==========================================
- Hits        20371    20367       -4     
- Misses      11560    11563       +3     
- Partials     1685     1686       +1     

see 8 files with indirect coverage changes

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