fix!: improve pipeline validation for reserved names

[wass3r]

fixes go-vela/community#1054

marked as breaking because technically it will return an error in cases where it didn't before. these should be edge cases, and in those cases, users likely observed other strange behavior.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.96%. Comparing base (91ba0d5) to head (013c04f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1325      +/-   ##
==========================================
+ Coverage   56.92%   56.96%   +0.04%     
==========================================
  Files         643      643              
  Lines       36106    36143      +37     
==========================================
+ Hits        20553    20590      +37     
  Misses      14916    14916              
  Partials      637      637              

Files with missing lines	Coverage Δ
compiler/native/validate.go	100.00% <100.00%> (ø)

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