Use default arch in CI

[JoshuaLampert]

There are warnings (e.g., https://github.com/JoshuaLampert/KernelInterpolation.jl/actions/runs/12123430476) in the CI runs because we request x64 on a macOS runner with arm64. I propose to simply use the default architecture, i.e. to remove the arch argument. For the flag-name of the coveralls action I followed the example under coverallsapp/github-action#complete-parallel-job-example.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.65%. Comparing base (e70717d) to head (45ae8fc).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #107   +/-   ##
=======================================
  Coverage   98.65%   98.65%           
=======================================
  Files          46       46           
  Lines        1266     1266           
=======================================
  Hits         1249     1249           
  Misses         17       17           

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