Move to StyleCop.Analyzers.Unstable

[edumserrano]

The StyleCop.Analyzers package hasn't had a stable release since version 1.1.118 in 2019.

After reading DotNetAnalyzers/StyleCopAnalyzers#3826 and this comment from DotNetAnalyzers/StyleCopAnalyzers#3647, I decided to adopt the usage of StyleCop.Analyzers.Unstable instead of using a beta version of StyleCop.Analyzers.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.02%. Comparing base (ade6772) to head (40259a9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #199   +/-   ##
=======================================
  Coverage   91.02%   91.02%           
=======================================
  Files          44       44           
  Lines         479      479           
  Branches       51       51           
=======================================
  Hits          436      436           
  Misses         35       35           
  Partials        8        8           

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