Fix type for urlencode's doseq argument

[elacuesta]

Continuation of #4950 (#4950 (review))

[codecov]

Codecov Report

Merging #5073 (f147cea) into master (127a858) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head f147cea differs from pull request most recent head 9e7cbc0. Consider uploading reports for the commit 9e7cbc0 to get more accurate results

@@            Coverage Diff             @@
##           master    #5073      +/-   ##
==========================================
- Coverage   88.09%   88.07%   -0.02%     
==========================================
  Files         162      162              
  Lines       10347    10347              
  Branches     1504     1504              
==========================================
- Hits         9115     9113       -2     
- Misses        964      965       +1     
- Partials      268      269       +1     

Impacted Files	Coverage Δ
scrapy/commands/bench.py	100.00% <100.00%> (ø)
scrapy/core/downloader/__init__.py	90.97% <0.00%> (-1.51%)	⬇️

[kmike]

Thanks for the follow-up @elacuesta!