GROOVY-11627: SC: disable mixed public and private overloads checking

[eric-milles]

I kept tests for the error and changed the trait test to work. It looked like the better example of a supported scenario.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 85.71429% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.0093%. Comparing base (b70de71) to head (85a4689).
⚠️ Report is 746 commits behind head on master.

Files with missing lines	Patch %	Lines
src/main/java/groovy/lang/MetaClassImpl.java	84.2105%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@                Coverage Diff                 @@
##               master      #2223        +/-   ##
==================================================
+ Coverage     69.0020%   69.0093%   +0.0073%     
- Complexity      29668      29670         +2     
==================================================
  Files            1423       1423                
  Lines          114317     114315         -2     
  Branches        19830      19830                
==================================================
+ Hits            78881      78888         +7     
+ Misses          28803      28798         -5     
+ Partials         6633       6629         -4     

Files with missing lines	Coverage Δ
...ehaus/groovy/classgen/ClassCompletionVerifier.java	84.1418% <100.0000%> (+0.0296%)	⬆️
src/main/java/groovy/lang/MetaClassImpl.java	78.2633% <84.2105%> (+0.0192%)	⬆️

... and 3 files with indirect coverage changes

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