fix(ci): use macOS 15 for Apple Silicon releases
Merged
DR
3d ago+4+4+0123456789-0-0-0123456789
The v0.2.11 release was blocked by the macOS 14 runner brownout. Configure cargo-dist to use macos-15 for aarch64-apple-darwin builds. The release workflow already reads its runner matrix from cargo-dist, so no workflow change is needed.
Validation: cargo-dist 0.30.3 plan succeeded and selects macos-15 for Apple Silicon; git diff --check passed. No version bump is included.