Fix predicate and add missing import

aleksis/apps/tezor/predicates.py

@@ -4,6 +4,8 @@ from rules import predicate
 
 from .models.invoice import Invoice
 
+User = get_user_model()
+
 @predicate
 def is_own_invoice(user: User, obj: Invoice):
     """Predicate which checks if the invoice is linked to the current user."""
@@ -14,10 +16,10 @@ def has_no_payment_variant(user: User, obj: Invoice):
     """Predicate which checks that the invoice has no payment variant."""
     return not obj.variant
 
-@predicate
 def is_in_payment_status(status: str):
     """Predicate which checks whether the invoice is in a specific state."""
 
+    @predicate
     def _predicate(user: User, obj: Invoice):
         return obj.status == status