Updated to transport.loseConnection()

[gabrielztk]

Resolves #4991 comment

Thanks! There are two additional occurrences:

* https://github.com/scrapy/scrapy/blob/2.4.1/scrapy/core/downloader/handlers/http11.py#L404

* https://github.com/scrapy/scrapy/blob/2.4.1/scrapy/core/downloader/handlers/http11.py#L523

[codecov]

Codecov Report

Merging #4995 (60a4aef) into master (da9a2f8) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 60a4aef differs from pull request most recent head 0ae66cb. Consider uploading reports for the commit 0ae66cb to get more accurate results

@@            Coverage Diff             @@
##           master    #4995      +/-   ##
==========================================
- Coverage   88.69%   88.69%   -0.01%     
==========================================
  Files         162      162              
  Lines       10967    10966       -1     
  Branches     1797     1796       -1     
==========================================
- Hits         9727     9726       -1     
  Misses        960      960              
  Partials      280      280              

Impacted Files	Coverage Δ
scrapy/core/downloader/handlers/http11.py	94.09% <100.00%> (-0.02%)	⬇️

[Gallaecio]

Note: This change is not needed until we drop support for Twisted 18.4.0, which may not happen in a while.

[kmike]

We now require Twisted 18.9.0+ (since #5514), so that's fine to proceed with this PR.