fix: use correct path separator in SARIF output when on Windows

[G-Rath]

Currently we always output a Unix path separator even when on Windows - this changes us to use the path separator based on the OS.

Resolves #604

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 68.24%. Comparing base (9cb6791) to head (c8293cf). Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1294   +/-   ##
=======================================
  Coverage   68.24%   68.24%           
=======================================
  Files         178      178           
  Lines       17234    17235    +1     
=======================================
+ Hits        11761    11762    +1     
  Misses       4833     4833           
  Partials      640      640           

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