refactor(notifications): Improve transactional email settings handling

- Replace `! $type` checks with `blank($type)` for consistency
- Modify email settings configuration to handle null/disabled states
- Ensure proper fallback and configuration of email providers

app/Notifications/Channels/EmailChannel.php

@@ -50,11 +50,9 @@ class EmailChannel
 
         if ($emailSettings->use_instance_email_settings) {
             $type = set_transanctional_email_settings();
-            if (! $type) {
+            if (blank($type)) {
                 throw new Exception('No email settings found.');
             }
-            config()->set('mail.default', $type);
-
             return;
         }