Install XQuartz under macOS

Author: nanxstats

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

@@ -33,6 +33,10 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      # To support plotting with SVG device under macOS
+      - if: runner.os == 'macOS'
+        run: brew install --cask xquartz
+
       - uses: r-lib/actions/setup-pandoc@v2
 
       - uses: r-lib/actions/setup-r@v2