Use StringComparison.Ordinal when locating token indices in PlaceMarkersUsfmUpdateBlockHandler

[Enkidu93]

Fixes #492.

I believe that using Ordinal is safe since the tokenizer doesn't do any normalization of combining characters I don't think.

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This change is 

[pmachapman]

@pmachapman reviewed 2 files and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on ddaspit).

[ddaspit]

@ddaspit reviewed 2 files and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on Enkidu93).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.52%. Comparing base (ae09770) to head (b98b21d).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #496      +/-   ##
==========================================
+ Coverage   73.51%   73.52%   +0.01%     
==========================================
  Files         451      451              
  Lines       37692    37697       +5     
  Branches     5183     5183              
==========================================
+ Hits        27708    27718      +10     
+ Misses       8845     8841       -4     
+ Partials     1139     1138       -1     

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