Adjust h2 version requirement

[elacuesta]

Closes #5058, fixes #5059

Taken from Twisted[http2]. The current h2>=3.2.0 results in the installation of the latest h2==4.0.0, which then gets uninstalled because it doesn't comply with the Twisted constraints.

@Gallaecio @wRAR @kmike Not exactly what we discussed, but it works nonetheless.

[Gallaecio]

I think we should either leave >=3.2.0 as the lower end or also change https://github.com/scrapy/scrapy/blob/master/tox.ini#L74

[codecov]

Codecov Report

Merging #5066 (2d39655) into master (f0e1a33) will decrease coverage by 1.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5066      +/-   ##
==========================================
- Coverage   88.01%   86.83%   -1.18%     
==========================================
  Files         162      162              
  Lines       10301    10295       -6     
  Branches     1501     1500       -1     
==========================================
- Hits         9066     8940     -126     
- Misses        965     1084     +119     
- Partials      270      271       +1     

Impacted Files	Coverage Δ
scrapy/pipelines/images.py	28.07% <0.00%> (-62.29%)	⬇️
scrapy/utils/asyncgen.py	80.00% <0.00%> (-20.00%)	⬇️
scrapy/utils/ssl.py	53.65% <0.00%> (-17.08%)	⬇️
scrapy/utils/test.py	50.00% <0.00%> (-10.94%)	⬇️
scrapy/utils/reactor.py	75.00% <0.00%> (-6.67%)	⬇️
scrapy/pipelines/media.py	91.48% <0.00%> (-5.68%)	⬇️
scrapy/extensions/feedexport.py	91.00% <0.00%> (-4.32%)	⬇️
scrapy/core/scraper.py	87.11% <0.00%> (-2.46%)	⬇️
scrapy/core/downloader/__init__.py	90.97% <0.00%> (-1.51%)	⬇️
scrapy/crawler.py	87.15% <0.00%> (-1.12%)	⬇️
... and 6 more

[elacuesta]

Makes sense, let's see if the pinned envs work with h2==3.0 and if that's the case, let's stick with it.