Install favicon build dependencies in GHA

Author: klmr

.github/workflows/build.yaml

@@ -50,6 +50,11 @@ jobs:
         with:
           ref: build
 
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y inkscape pngcrush
+
       - uses: r-lib/actions/setup-r@v2
 
       - uses: r-lib/actions/setup-r-dependencies@v2