[MOV] website_portal: move mail portal tests directly to mail

Those belong to mail, not website_portal.

addons/mail/tests/__init__.py

@@ -11,3 +11,4 @@ from . import test_mail_template
 from . import test_invite
 from . import test_ir_actions
 from . import test_update_notification
+from . import test_portal

addons/portal/tests/__init__.py

@@ -2,4 +2,3 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from . import test_load_process
-from . import test_portal