fix(compiler): validate yaml.Build post-expansion and fully validate step image

[ecrupper]

Closes go-vela/community#899

I think the real error in the issue is the fact that the pipeline passes validation more so than the repo counter not being updated. By not immediately validating the pipeline after unmarshaling, and rather waiting for the final expansion to validate, we don't need to specify && len(step.Template.Name) == 0 .

This should result in an audit error rather than a build error — thus, no build.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (78eca51) 67.04% compared to head (99b65f8) 67.03%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1036      +/-   ##
==========================================
- Coverage   67.04%   67.03%   -0.01%     
==========================================
  Files         330      330              
  Lines       14092    14088       -4     
==========================================
- Hits         9448     9444       -4     
  Misses       4165     4165              
  Partials      479      479              

Files	Coverage Δ
compiler/native/compile.go	67.56% <ø> (-0.35%)	⬇️
compiler/native/validate.go	96.42% <100.00%> (ø)