Pin aarch64-apple-darwin to macos-15 runner for PKCS12 compatibility

macOS 14 rejects OpenSSL 3.x p12 format; macos-15 handles it correctly.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: byshing

dist-workspace.toml

@@ -28,3 +28,6 @@ allow-dirty = ["ci"]
 
 [dist.dependencies.apt]
 libdbus-1-dev = "*"
+
+[dist.github-custom-runners]
+aarch64-apple-darwin = "macos-15"