[slang-tidy] Fix XilinxDoNotCareValues checker

[likeamahoney]

Following checker have a false positives because it is does not take into account the use of questions inside a comments.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.73%. Comparing base (f8042bf) to head (3e47343).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1225   +/-   ##
=======================================
  Coverage   94.73%   94.73%           
=======================================
  Files         205      205           
  Lines       51212    51212           
=======================================
  Hits        48518    48518           
  Misses       2694     2694           

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