add an integration test for 0-RTT GET requests

[marten-seemann]

Depends on #4379.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.91%. Comparing base (603e077) to head (d298ea2).
Report is 1 commits behind head on http3-dont-modify-0rtt-requests.

❗ Current head d298ea2 differs from pull request most recent head a367196. Consider uploading reports for the commit a367196 to get more accurate results

Additional details and impacted files

@@                         Coverage Diff                         @@
##           http3-dont-modify-0rtt-requests    #4380      +/-   ##
===================================================================
+ Coverage                            84.86%   84.91%   +0.04%     
===================================================================
  Files                                  151      151              
  Lines                                14337    14343       +6     
===================================================================
+ Hits                                 12167    12178      +11     
+ Misses                                1670     1666       -4     
+ Partials                               500      499       -1     

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