CI: stop using tox-pip-version

[Gallaecio]

Aims to fix #5388.

[Gallaecio]

I removed the only thing that the 2 failing jobs had in common that the other jobs did not have, and it has worked.

We introduced tox-pip-version in #5207 because otherwise CI would fail. The situation now is the opposite.

I think pypa/pip#10481 may be the reason we can now use the latest pip without issues.

[codecov]

Codecov Report

Merging #5389 (62f9d8e) into master (fe43411) will increase coverage by 0.15%.
The diff coverage is n/a.

❗ Current head 62f9d8e differs from pull request most recent head 669d4dc. Consider uploading reports for the commit 669d4dc to get more accurate results

@@            Coverage Diff             @@
##           master    #5389      +/-   ##
==========================================
+ Coverage   88.43%   88.59%   +0.15%     
==========================================
  Files         163      163              
  Lines       10651    10651              
  Branches     1816     1816              
==========================================
+ Hits         9419     9436      +17     
+ Misses        956      940      -16     
+ Partials      276      275       -1     

Impacted Files	Coverage Δ
scrapy/__main__.py	0.00% <0.00%> (-33.34%)	⬇️
scrapy/robotstxt.py	97.53% <0.00%> (+22.22%)	⬆️