ci: make canary run --arch=universal on macOS

[erickzhao]

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• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable).
• The testsuite passes successfully on my local machine (if applicable).

Summary

Our electron-nightly canary job runs the latest nightly version of Electron against the main branch of Electron Packager.

This job has been busted for a while, and it seems because --arch=all does not work on macOS ever since we. This is a separate issue, but for now, let's just create a single --arch=universal job so that we can unblock the canary.

Testing

See c7a3088 for that job running on this PR.

[codecov]

Codecov Report

Merging #1539 (aa10ea9) into main (5ee6d73) will not change coverage.
Report is 1 commits behind head on main.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1539   +/-   ##
=======================================
  Coverage   95.58%   95.58%           
=======================================
  Files          15       15           
  Lines         793      793           
=======================================
  Hits          758      758           
  Misses         35       35           

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[malept]

Seems good, just one nit