fix: main check when using gomod.proxy

[caarlos0]

we can't check for the main function in the actual proxied module, but we can at least check the code which, in theory, is the module being proxied.

this should avoid bad releases as I did for fork-cleaner, which was basically empty.

What happens now is that the gomod pipe overrides Main and Dir as before, but set the original values to UnproxiedMain and UnproxiedDir, and then the build pipe checks the main on the unproxied properties when they exist.

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[codecov]

Codecov Report

Merging #2390 (1471bd6) into master (1d90ecb) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2390      +/-   ##
==========================================
+ Coverage   82.91%   82.94%   +0.02%     
==========================================
  Files          83       83              
  Lines        6059     6067       +8     
==========================================
+ Hits         5024     5032       +8     
  Misses        887      887              
  Partials      148      148              

Impacted Files	Coverage Δ
pkg/config/config.go	90.72% <ø> (ø)
internal/builders/golang/build.go	92.89% <100.00%> (+0.20%)	⬆️
internal/pipe/gomod/gomod.go	78.44% <100.00%> (+0.37%)	⬆️

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[github-actions]

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