fix testdata runner

[crowlKats]

Taken from #718

[bors-servo]

☔ The latest upstream changes (presumably #751) made this pull request unmergeable. Please resolve the merge conflicts.

[codecov-commenter]

Codecov Report

Merging #752 (a18a2a3) into master (c34de27) will increase coverage by 0.02%.
The diff coverage is 63.15%.

@@            Coverage Diff             @@
##           master     #752      +/-   ##
==========================================
+ Coverage   85.23%   85.25%   +0.02%     
==========================================
  Files          22       22              
  Lines        3880     3886       +6     
==========================================
+ Hits         3307     3313       +6     
  Misses        573      573              

Impacted Files	Coverage Δ
url/tests/data.rs	75.65% <63.15%> (+1.34%)	⬆️

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