CI: updates to fix publishing universal darwin binaries

[onetechnical]

Summary

Some parts of the release pipeline do not account for the change in naming for the universal darwin binary. This PR addresses this.

Note that we also copy the universal binary to arch-specific named files. This is for backwards compatibility with the update.sh script.

The signing script in particular should run across all installs, as it handles it from a single platform. This means the host identifier is incorrect in this invocation.

Test Plan

Tested by manually running parts of this; should verify with the next stable release if merged before then.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.23%. Comparing base (c44aba5) to head (07c79c9).
Report is 1 commits behind head on rel/beta.

Additional details and impacted files

@@             Coverage Diff              @@
##           rel/beta    #6141      +/-   ##
============================================
- Coverage     56.48%   56.23%   -0.26%     
============================================
  Files           499      494       -5     
  Lines         70029    69954      -75     
============================================
- Hits          39556    39338     -218     
- Misses        27808    27937     +129     
- Partials       2665     2679      +14     

Flag	Coverage Δ
	56.23% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.