try installing X11 on MacOS

Author: dchiu911

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

@@ -30,6 +30,11 @@ jobs:
       R_KEEP_PKG_SOURCE: yes
 
     steps:
+      - name: Install X11 dependencies on MacOS
+        if: matrix.config.os == 'macos-latest'
+        run: |
+          brew --cask install xquartz
+
       - uses: actions/checkout@v4
 
       - uses: r-lib/actions/setup-pandoc@v2