Fix CI (pin older Scrapy).

[wRAR]

Some tests hang with new Scrapy due to scrapy/scrapy#6784

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.29%. Comparing base (703290b) to head (613dfab).
Report is 3 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #223       +/-   ##
===========================================
- Coverage   86.16%   56.29%   -29.87%     
===========================================
  Files          16       16               
  Lines        1048     1048               
===========================================
- Hits          903      590      -313     
- Misses        145      458      +313     

see 14 files with indirect coverage changes

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