Fix 'is pattern expression' parentheses handling

[sharwell]

Fixes #2372

[codecov]

Codecov Report

Merging #2424 into master will decrease coverage by 0.03%.
The diff coverage is 96.66%.

@@            Coverage Diff            @@
##           master   #2424      +/-   ##
=========================================
- Coverage   96.43%   96.4%   -0.04%     
=========================================
  Files         714     715       +1     
  Lines       92522   92551      +29     
  Branches     3444    3445       +1     
=========================================
- Hits        89226   89224       -2     
- Misses       2403    2434      +31     
  Partials      893     893

Impacted Files	Coverage Δ
...yzers/StyleCop.Analyzers.Test/WorkItemAttribute.cs	100% <100%> (ø)
...nalyzers/StyleCop.Analyzers.Test/AttributeTests.cs	100% <100%> (ø)	⬆️
...SA1119StatementMustNotUseUnnecessaryParenthesis.cs	90% <100%> (+0.09%)	⬆️
...rp7/MaintainabilityRules/SA1119CSharp7UnitTests.cs	55.71% <93.33%> (-44.29%)	⬇️

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