fix(Build Cop): only close duplicates when the test was run

[tbpg]

Otherwise, if there are 50 invocations of the bot at the same time, they
will all try to close the duplicate issues. This isn't perfect, but will
be way better than 50.

Fixes #283 🦕

[codecov]

Codecov Report

Merging #297 into master will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #297      +/-   ##
==========================================
+ Coverage   87.45%   87.50%   +0.04%     
==========================================
  Files          15       15              
  Lines        2687     2696       +9     
  Branches      268      270       +2     
==========================================
+ Hits         2350     2359       +9     
  Misses        324      324              
  Partials       13       13              

Impacted Files	Coverage Δ
packages/buildcop/src/buildcop.ts	94.47% <0.00%> (+0.10%)	⬆️
packages/generate-bot/main.js	74.01% <0.00%> (ø)	⬆️
packages/publish/src/publish.ts	70.83% <0.00%> (ø)	⬆️
packages/gcf-utils/src/gcf-utils.ts	77.94% <0.00%> (ø)	⬆️
packages/auto-label/src/auto-label.ts	81.57% <0.00%> (ø)	⬆️
packages/label-sync/src/label-sync.ts	80.15% <0.00%> (ø)	⬆️
packages/release-please/src/runner.ts	84.61% <0.00%> (ø)	⬆️
packages/blunderbuss/src/blunderbuss.ts	90.34% <0.00%> (ø)	⬆️
packages/failurechecker/src/failurechecker.ts	93.93% <0.00%> (ø)	⬆️
packages/merge-on-green/src/merge-on-green.ts	94.37% <0.00%> (ø)	⬆️
... and 5 more

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[nnegrey]

LGTM