Use Chromium binary from system for capturing screenshots

This commit makes screenshot tests work on macOS running on Apple silicon at
the cost of adding Chromium as an external dependency.

See puppeteer/puppeteer#6622 for more details.

runScreenshotTests

@@ -50,6 +50,8 @@ do
     test_details="Target path: $(magenta $target_path) | "
     test_details+="Viewport width: $(magenta $viewport_width)"
     echo -en "[$(gray ....)] ${test_details} "
+    PUPPETEER_EXECUTABLE_PATH=$(which chromium) \
+    PUPPETEER_SKIP_CHROMIUM_DOWNLOAD=true \
     ./comparePages $target_path $viewport_width && {
       echo -e "\r[$(bold_green PASS)] ${test_details}"
     } || {