Fix CI: update macOS runner from retired macos-13 to macos-15

Author: caseymanos

.github/workflows/prebuild.yml

@@ -14,7 +14,7 @@ jobs:
       matrix:
         include:
           # macOS
-          - os: macos-13  # Intel
+          - os: macos-15  # Intel (macos-13 retired)
             arch: x64
           - os: macos-14  # Apple Silicon
             arch: arm64