Fix dev builds upload to match links used in manifest

[wojtekn]

Related to https://github.com/Automattic/dotcom-forge/issues/7339

Proposed Changes

I propose to:

• add 'universal' in links generated in manifest to match file names used when uploading binaries to CDN:

  studio/fastlane/Fastfile

  Line 95 in 1fe21c8

  filename_core: 'darwin-universal',

• fix the binary upload code to use short sha instead of full one to match links used in manifest:

  studio/scripts/generate-releases-manifest.mjs

  Line 47 in 1fe21c8

  const currentCommit = child_process.execSync( 'git rev-parse --short HEAD' ).toString().trim();

Testing Instructions

Test if the dev builds links in manifest work after emerging this PR.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?