Auto use grub2 mode for krd.iso

INSTALL/grub/grub.cfg

@@ -746,7 +746,16 @@ function uefi_linux_menu_func {
         ventoy_acpi_param ${vtoy_chain_mem_addr} 2048
         ventoy_cli_console     
 
+        unset vtGrub2Mode
         if vt_check_mode 3; then
+            set vtGrub2Mode=1
+        elif vt_str_begin "$vt_volume_id" "KRD"; then
+            if [ -f (loop)/boot/grub/grub.cfg.sig ]; then
+                set vtGrub2Mode=1
+            fi
+        fi
+
+        if [ -n "$vtGrub2Mode" ]; then
             ventoy_debug_pause
         else
             if [ "$VTOY_EFI_ARCH" != "mips" ]; then