[eas-json] mark Xcode 15 image as default

[szdziedzic]

Why

Companion to https://github.com/expo/turtle-v2/pull/1733

How

mark Xcode 15 image as default

[github-actions]

❌ It looks like a changelog entry is missing for this PR. You have two options: you can add it manually, or you can use the changelog bot to do it for you.
🤖 To use the bot, simply comment on this PR with the command /changelog-entry [breaking-change|new-feature|bug-fix|chore] [message].
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[github-actions]

Size Change: -781 B (0%)

Total Size: 51.3 MB

Filename	Size	Change
./packages/eas-cli/dist/eas-linux-x64.tar.gz	51.3 MB	-781 B (0%)

_{compressed-size-action}

[szdziedzic]

/changelog-entry Mark the macos-ventura-13.6-xcode-15.2 image as default in the eas.json schema

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.99%. Comparing base (33fb5fa) to head (0851423).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2278   +/-   ##
=======================================
  Coverage   53.99%   53.99%           
=======================================
  Files         520      520           
  Lines       18981    18981           
  Branches     3813     3813           
=======================================
  Hits        10247    10247           
  Misses       8713     8713           
  Partials       21       21           

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