Don't emit CA1861 for static ReadOnlyCollections

[CollinAlpert]

This PR excludes static readonly ReadOnlyCollections from triggering CA1861. Fixes #6629.

[codecov]

Codecov Report

Merging #6644 (befdc3a) into main (c2fd19b) will decrease coverage by 0.01%.
The diff coverage is 82.22%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6644      +/-   ##
==========================================
- Coverage   96.40%   96.39%   -0.01%     
==========================================
  Files        1377     1379       +2     
  Lines      322008   322186     +178     
  Branches    10434    10459      +25     
==========================================
+ Hits       310438   310585     +147     
- Misses       9081     9109      +28     
- Partials     2489     2492       +3     

[buyaa-n]

Thank you @CollinAlpert for the fix, with the feedback on the issue:

If you're assigning to a static, you're already publishing it to be shared / reused, regardless of whether that static is readonly. And lazy initialization is a key place where you assign to statics and we don't want false positives

Now we want to exclude any static field initializations, please update the PR accordingly

[buyaa-n]

Now we want to exclude any static field initializations, please update the PR accordingly

OK, updated myself as I need this fix