fix(bundler): add default value for xdg_mime env var (#8742)

tooling/bundler/src/bundle/linux/templates/appimage

@@ -7,6 +7,7 @@ set -euxo pipefail
 
 export ARCH={{arch}}
 APPIMAGE_BUNDLE_XDG_OPEN=${APPIMAGE_BUNDLE_XDG_OPEN-0}
+APPIMAGE_BUNDLE_XDG_MIME=${APPIMAGE_BUNDLE_XDG_MIME-0}
 APPIMAGE_BUNDLE_GSTREAMER=${APPIMAGE_BUNDLE_GSTREAMER-0}
 TAURI_TRAY_LIBRARY_PATH=${TAURI_TRAY_LIBRARY_PATH-0}