action: update command to remove docker image

Author: yanxin152133

.github/workflows/openwrt-ci.yml

@@ -27,7 +27,7 @@ jobs:
         env:
           DEBIAN_FRONTEND: noninteractive
         run: |
-          docker rmi `docker images -q`
+          docker image prune -f
           sudo -E rm -rf /usr/share/dotnet /etc/mysql /etc/php /etc/apt/sources.list.d /usr/local/lib/android
           sudo -E apt-mark hold grub-efi-amd64-signed
           sudo -E apt update