CI test on both intel and arm64 MacOS

Author: jeroen

.github/workflows/R-CMD-check.yaml

@@ -19,7 +19,7 @@ jobs:
       fail-fast: false
       matrix:
         config:
-          - {os: macos-14,        r: 'release'}
+          - {os: macos-15-intel,  r: 'release'}
           - {os: macos-latest,    r: 'next'}
           - {os: windows-latest,  r: '4.1'}
           - {os: windows-latest,  r: '4.2'}