Currently CI uses the org's self-hosted (in macstadium) macOS runners (macOS-10.15-X64, macOS-11-ARM64), but we'd prefer to not have to pay for and maintain the machines if we can.

We should:

• replace the usage with Github-hosted runners if we can
• attempt to do a nice deprecation phasing (maybe including on the Pants-side, too)

Refs:

• Test and release on newer macOS: 13 (x86-64) and 14 (arm64) pants#21655
• Upgrade CI to build on macOS 12 pants#21413
• Proposal: consider dropping support for macOS 10.15 & macOS 11 pants#21074