Fix SA1515 handling of comment after pattern-matching case label

[sharwell]

Fixes #2462.

[codecov]

Codecov Report

Merging #2461 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2461      +/-   ##
==========================================
+ Coverage   97.28%   97.28%   +<.01%     
==========================================
  Files         734      735       +1     
  Lines       94977    94995      +18     
  Branches     3470     3470              
==========================================
+ Hits        92396    92414      +18     
  Misses       1741     1741              
  Partials      840      840

Impacted Files	Coverage Δ
...Test.CSharp7/LayoutRules/SA1515CSharp7UnitTests.cs	100% <100%> (ø)
...A1515SingleLineCommentMustBePrecededByBlankLine.cs	95.65% <100%> (+0.03%)	⬆️

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[AArnott]

Fixes #2462