Update CI a bit

Author: jeroen

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

@@ -28,8 +28,8 @@ jobs:
       fail-fast: false
       matrix:
         config:
-          - {os: macos-13,       r: 'release'}
-          - {os: macos-latest,   r: 'release'}
+          - {os: macos-14,       r: 'release'}
+          - {os: macos-15-intel, r: 'release'}
           - {os: windows-latest, r: 'release'}
           - {os: windows-latest, r: 'oldrel-1'}
           - {os: windows-latest, r: 'oldrel-2'}