🎨(ruff) fix linter error after ruff update

Fix the `make lint` errors after dependencies update.

src/backend/mailbox_manager/admin.py

@@ -11,7 +11,6 @@ from mailbox_manager import enums, models
 from mailbox_manager.utils.dimail import DimailAPIClient
 
 # Prevent Ruff complaining about mark_safe below
-# ruff: noqa: S308
 
 
 @admin.action(description=_("Import emails from dimail"))

src/backend/mailbox_manager/apps.py

@@ -15,4 +15,5 @@ class MailboxManagerConfig(AppConfig):
         """
         Import signals when the app is ready.
         """
-        import mailbox_manager.signals  # pylint: disable=import-outside-toplevel, unused-import
+        # pylint: disable=import-outside-toplevel, unused-import
+        import mailbox_manager.signals  # noqa: PLC0415