chore(ci): split linter into its own job

[jansegre]

Not intended to merge right now, but we can look into this.

[codecov[bot]]

Codecov Report

Merging #349 (86bd10f) into dev (9fe53b5) will increase coverage by 0.01%. The diff coverage is n/a.

@@            Coverage Diff             @@
##              dev     #349      +/-   ##
==========================================
+ Coverage   82.16%   82.17%   +0.01%     
==========================================
  Files         153      153              
  Lines       14481    14481              
  Branches     2085     2085              
==========================================
+ Hits        11898    11900       +2     
+ Misses       2156     2155       -1     
+ Partials      427      426       -1     

Impacted Files	Coverage Δ
hathor/pubsub.py	93.87% <0.00%> (+4.08%)	:arrow_up:

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