[CI] Use M1 runners for macOS-based GH Actions workflows

Summary:
Context: https://github.blog/changelog/2024-01-30-github-actions-introducing-the-new-m1-macos-runner-available-to-open-source/

Should speed up iOS/macOS builds and reduce time from kicking off release to it being available via Internal TestFlight.

Test Plan: Hoping that it just works, will revert if any issues arise.

Reviewers: ashoat, ginsu, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D10967