Pi kiosk: add --test-type to hide Chromium unsupported-flag banner

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/kiosk.sh

@@ -10,4 +10,5 @@ exec "$BIN" \
   --overscroll-history-navigation=0 \
   --ozone-platform=wayland \
   --ignore-gpu-blocklist \
+  --test-type \
   "$URL" >/tmp/chromium-kiosk.log 2>&1