Add imagemagick to GA workflow so magick package can be used

.github/workflows/quarto-gh-pages-html.yml

@@ -30,6 +30,9 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
+      - name: Install ImageMagick
+        run: sudo apt-get install -y libmagick++-dev
+
       - uses: r-lib/actions/setup-r@v2
         with:
           use-public-rspm: true