chore: split actions to tests and linting

[rdimitrov]

The following PR:

• Splits the workflows to one for linting and one for tests
• Updates some of the action's settings to address issues like https://github.com/rdimitrov/go-tuf-metadata/actions/runs/7129104975/job/19412986382#step:5:88
• Added a threshold of allowed 5% decrease in test coverage for PRs before marking Codecov's status as failed
• Disabled codecov/patch status since it makes PRs harder to review

Fixes #88

[codecov]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (b466701) 71.68% compared to head (ce6072f) 71.65%.
Report is 2 commits behind head on main.

Files	Patch %	Lines
metadata/updater/updater.go	66.66%	6 Missing ⚠️
metadata/logger.go	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #89      +/-   ##
==========================================
- Coverage   71.68%   71.65%   -0.03%     
==========================================
  Files          10       10              
  Lines        1974     1976       +2     
==========================================
+ Hits         1415     1416       +1     
- Misses        452      453       +1     
  Partials      107      107              

Flag	Coverage Δ
Go-1.21	71.65% <86.53%> (-0.03%)	⬇️

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[rdimitrov]

cc @kommendorkapten