Update CI to support Twisted 21.2.0

[Gallaecio]

Fixes #5020

[Gallaecio]

The remaining failures are about #5017, https://twistedmatrix.com/trac/ticket/10106

[codecov]

Codecov Report

Merging #5027 (5edc48a) into master (42e4dbb) will decrease coverage by 0.20%.
The diff coverage is 90.00%.

❗ Current head 5edc48a differs from pull request most recent head 1667583. Consider uploading reports for the commit 1667583 to get more accurate results

@@            Coverage Diff             @@
##           master    #5027      +/-   ##
==========================================
- Coverage   87.82%   87.62%   -0.21%     
==========================================
  Files         158      162       +4     
  Lines        9736    10288     +552     
  Branches     1435     1499      +64     
==========================================
+ Hits         8551     9015     +464     
- Misses        929     1001      +72     
- Partials      256      272      +16     

Impacted Files	Coverage Δ
scrapy/utils/log.py	89.24% <ø> (ø)
scrapy/pipelines/images.py	90.35% <80.00%> (-1.47%)	⬇️
scrapy/core/http2/protocol.py	83.41% <83.41%> (ø)
scrapy/core/downloader/contextfactory.py	87.03% <84.61%> (-2.97%)	⬇️
scrapy/core/http2/stream.py	91.37% <91.37%> (ø)
scrapy/core/http2/agent.py	96.38% <96.38%> (ø)
scrapy/core/downloader/handlers/http11.py	93.85% <100.00%> (+1.16%)	⬆️
scrapy/core/downloader/handlers/http2.py	100.00% <100.00%> (ø)
scrapy/utils/asyncgen.py	80.00% <0.00%> (-20.00%)	⬇️
scrapy/utils/ssl.py	53.65% <0.00%> (-17.08%)	⬇️
... and 10 more