Allow saving bookmarks with authenticated URLs

Bookmarks behind authentication couldn't be saved.
The app didn't allow saving when URL metadata check failed, even
though Linkding accepts these URLs.
The error message still displays to inform users that metadata
couldn't be fetched, but it no longer blocks saving.

lib/i18n/strings_es.i18n.json

@@ -74,7 +74,7 @@
       "validateUrl": "Validar URL",
       "urlValid": "La URL es válida",
       "urlNotValid": "La URL no es válida",
-      "cannotCheckUrl": "No se pudo comprobar la URL",
+      "cannotCheckUrl": "No se pudo comprobar la URL, pero puedes guardarla de todas formas.",
       "invalidUrl": "URL no válida",
       "checkingUrl": "Comprobando URL...",
       "title": "Title",