fix flaky 0-RTT integration test

[marten-seemann]

No description provided.

[codecov]

Codecov Report

Merging #3224 (9794b6d) into master (2054732) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3224      +/-   ##
==========================================
+ Coverage   85.43%   85.44%   +0.01%     
==========================================
  Files         133      133              
  Lines        9807     9807              
==========================================
+ Hits         8378     8379       +1     
+ Misses       1057     1056       -1     
  Partials      372      372              

Impacted Files	Coverage Δ
internal/utils/rand.go	75.00% <0.00%> (+12.50%)	⬆️

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