[eas-cli] use BuildMode.REPACK for --repack builds

[szdziedzic]

Why

use BuildMode.REPACK for --repack builds

How

use BuildMode.REPACK for --repack builds

Test Plan

run repack build locally

[github-actions]

Size Change: -397 B (0%)

Total Size: 51.3 MB

Filename	Size	Change
./packages/eas-cli/dist/eas-linux-x64.tar.gz	51.3 MB	-397 B (0%)

_{compressed-size-action}

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 53.41%. Comparing base (466339b) to head (dd102e6).

Files	Patch %	Lines
packages/eas-cli/src/build/android/prepareJob.ts	0.00%	6 Missing ⚠️
packages/eas-cli/src/build/ios/prepareJob.ts	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2390      +/-   ##
==========================================
- Coverage   53.43%   53.41%   -0.02%     
==========================================
  Files         530      530              
  Lines       19516    19526      +10     
  Branches     3963     3967       +4     
==========================================
  Hits        10427    10427              
- Misses       8337     8347      +10     
  Partials      752      752              

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[github-actions]

⏩ The changelog entry check has been skipped since the "no changelog" label is present.