fix: use target platform path separators for asar integrity keys

[MarshallOfSound]

After the resedit change cross-building windows on macOS is suddenly a Thing People Can Do so we need to make sure we use windows path separators for the asar integrity manifest when targeting the windows platform.

Fixes #1780

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.66%. Comparing base (7024c67) to head (4fe36b1).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/platform.ts	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1781      +/-   ##
==========================================
- Coverage   89.08%   88.66%   -0.42%     
==========================================
  Files          17       17              
  Lines         907      909       +2     
  Branches      187      188       +1     
==========================================
- Hits          808      806       -2     
- Misses         62       64       +2     
- Partials       37       39       +2     

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[continuous-auth]

🎉 This PR is included in version 18.3.6 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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