Remove -dev from python-version

[abhinavsingh]

See https://twitter.com/imoracle/status/1224070108064043008 for background

[codecov]

Codecov Report

Merging #287 into develop will increase coverage by 2.21%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #287      +/-   ##
===========================================
+ Coverage    73.06%   75.27%   +2.21%     
===========================================
  Files           74       72       -2     
  Lines         2848     2771      -77     
===========================================
+ Hits          2081     2086       +5     
+ Misses         767      685      -82

Impacted Files	Coverage Δ
proxy/core/ssh/tunnel.py	0% <0%> (ø)	⬆️
proxy/http/parser.py	95.51% <0%> (+1.28%)	⬆️
proxy/http/handler.py	79.07% <0%> (+0.08%)	⬆️
proxy/proxy.py	87.75% <0%> (+0.25%)	⬆️
proxy/testing/test_case.py	60.78% <0%> (+0.78%)	⬆️

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[abhinavsingh]

@Benouare jFYI, this fixes incompatible Python versions used by GH actions.