sip: provider: Don't warn when trying to add account multiple times

A g_debug() will suffice which will let us get rid of g_test_expect_message() to
as we don't need to guard against the warning anymore.

plugins/sip/calls-sip-provider.c

@@ -469,7 +469,8 @@ calls_sip_provider_add_origin (CallsSipProvider *self,
     g_autofree char *name = NULL;
     g_object_get (credentials, "name", &name, NULL);
 
-    g_warning ("Cannot add credentials with name '%s' multiple times", name);
+    /* This could be a INFO level log once we have improved logging */
+    g_debug ("Cannot add credentials with name '%s' multiple times", name);
     return NULL;
   }