Fix array encoding in form data requests

[imiric]

This is a continuation of #1754, with an added check for the correct encoding and disabling of the exhaustive linter, since it doesn't seem like we can avoid the reflection.

Closes #1713

[codecov-commenter]

Codecov Report

Merging #2060 (89a6da9) into master (5b44097) will decrease coverage by 0.06%.
The diff coverage is 100.00%.

❗ Current head 89a6da9 differs from pull request most recent head c7bb596. Consider uploading reports for the commit c7bb596 to get more accurate results

@@            Coverage Diff             @@
##           master    #2060      +/-   ##
==========================================
- Coverage   71.97%   71.91%   -0.07%     
==========================================
  Files         181      179       -2     
  Lines       14139    14137       -2     
==========================================
- Hits        10177    10167      -10     
- Misses       3338     3343       +5     
- Partials      624      627       +3     

Flag	Coverage Δ
ubuntu	71.91% <100.00%> (+0.02%)	⬆️
windows	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
js/modules/k6/http/request.go	83.80% <100.00%> (+0.15%)	⬆️
js/common/initenv.go	66.66% <0.00%> (-33.34%)	⬇️
lib/netext/httpext/error_codes.go	94.52% <0.00%> (-2.74%)	⬇️
js/initcontext.go	90.42% <0.00%> (-2.13%)	⬇️
lib/netext/httpext/request.go	93.33% <0.00%> (-0.61%)	⬇️
js/runner.go	82.25% <0.00%> (-0.57%)	⬇️
lib/netext/httpext/error_codes_syscall_windows.go
cmd/ui_windows.go

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[mstoykov]

LGTM!

I would've used a range as it seems more idiomatic to me but this is fine as well

[imiric]

Apparently 2 approvals are required if a previous approval was dismissed? :-/