CI: upgrade workflows to use macos-15-large rather than macos-13

[marcelosalloum]

What

Upgrade workflows to use macos-latest and macos-15-large rather than macos-13

Why

1. It's about to be deprecated: announcement 🔗
2. It's already making the CI fail: example run 🔗

Notes on Runner Compatibility

After extensive testing across macOS runner types:

Runner	Result	Notes
✅ macos-15-large	✅ Passes	Stable with full setup.
✅ macos-14	✅ Passes	Works consistently.
🟠 macos-15-intel	⚠️ Unreliable	Passed in a minimal setup but failed under full load — switched to -large for stability.
❌ macos-15	❌ Fails	Does not support nested virtualization (required by Lima/QEMU).

[leighmcculloch]

9d9a3ed which was running with macos-15-intel looks like it was working fine, but got canceled, but at build and test did pass. Why use macos-15-large instead of it?

[marcelosalloum]

9d9a3ed which was running with macos-15-intel looks like it was working fine, but got canceled, but at build and test did pass. Why use macos-15-large instead of it?

Here's why:

• https://github.com/stellar/quickstart/pull/819/commits/9d9a3ed68ec0b7bdd94038fb09d81afa22e49171 (on macos-15-intel) didn't pass within ~45min, and it didn't seem like it was making any progress. In other tests, this usually resulted inn timeouts at 1h.
• https://github.com/stellar/quickstart/pull/819/commits/c15984870663bffe1549d1cddded62e6f6799cd5 (on macos-15-large) passed in less than 10min