Fix deprecated 'brew cask' calls

brew cask is now deprecated in favor of the `--cask` argument

Author: jimhester

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

@@ -78,7 +78,7 @@ jobs:
         if: runner.os == 'macOS'
         run: |
           # XQuartz is needed by vdiffr
-          brew cask install xquartz
+          brew install --cask xquartz
 
           # Use only binary packages
           echo 'options(pkgType = "binary")' >> ~/.Rprofile

.github/workflows/test-coverage.yaml

@@ -41,7 +41,7 @@ jobs:
       - name: Install system dependencies on macOS
         run: |
           # XQuartz is needed by vdiffr
-          brew cask install xquartz
+          brew install --cask xquartz
 
       - name: Install dependencies
         run: |