fix(prepare): destFile path separator

[erisu]

Motivation and Context

Resolves #1454

Description

Update the destFile variable to use the correct platform-specific path segment separators.

Testing

npm t

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[codecov-commenter]

Codecov Report

Merging #1455 (5fd8aee) into master (f38e8eb) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1455   +/-   ##
=======================================
  Coverage   72.25%   72.25%           
=======================================
  Files          21       21           
  Lines        1748     1748           
=======================================
  Hits         1263     1263           
  Misses        485      485           

Impacted Files	Coverage Δ
lib/prepare.js	46.63% <100.00%> (ø)

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[NiklasMerz]

Code LGTM

[NelsonChad]

Hi ,when i run cordova platform add android@11.0.0 I'm getting this error in prepare.js file

TypeError: Cannot read properties of null (reading 'find')
at E:\DEV\IONIC\donateApp_cord\node_modules\cordova-android\lib\prepare.js:387:49
at Array.forEach (<anonymous>)
at updateProjectSplashScreen (E:\DEV\IONIC\donateApp_cord\node_modules\cordova-android\lib\prepare.js:384:7)
at updateProjectAccordingTo (E:\DEV\IONIC\donateApp_cord\node_modules\cordova-android\lib\prepare.js:269:5)
at E:\DEV\IONIC\donateApp_cord\node_modules\cordova-android\lib\prepare.js:67:21
at processTicksAndRejections (node:internal/process/task_queues:96:5)
at async Promise.all (index 0)
[ERROR] An error occurred while running subprocess cordova.

can you help me please?