Update the checking workflow: add a library to check tcltk on macOS

Author: aursiber

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

@@ -42,6 +42,11 @@ jobs:
           http-user-agent: ${{ matrix.config.http-user-agent }}
           use-public-rspm: true
 
+      - name: Install libraries for macOS
+        if: runner.os == 'macOS'
+        run: |
+          brew install xquartz
+
       - uses: r-lib/actions/setup-r-dependencies@v2
         with:
           pak-version: devel