fix: setHeader loop with array

[czy88840616]

fix: #690

[gitpod-io]

[codecov-io]

Codecov Report

Merging #691 into 2.x will increase coverage by 0.09%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              2.x     #691      +/-   ##
==========================================
+ Coverage   87.18%   87.28%   +0.09%     
==========================================
  Files          96       96              
  Lines        4120     4120              
  Branches      686      687       +1     
==========================================
+ Hits         3592     3596       +4     
+ Misses        515      511       -4     
  Partials       13       13              

Impacted Files	Coverage Δ
packages/web-koa/src/framework.ts	77.86% <100.00%> (+3.27%)	⬆️

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