specify unit for invitation expiration

tests/domain/test_invitations.py

@@ -27,7 +27,7 @@ def test_accept_invitation():
 def test_accept_expired_invitation():
     workspace = WorkspaceFactory.create()
     user = UserFactory.create()
-    increment = Invitations.EXPIRATION_LIMIT + 1
+    increment = Invitations.EXPIRATION_LIMIT_MINUTES + 1
     created_at = datetime.datetime.now() - datetime.timedelta(minutes=increment)
     invite = InvitationFactory.create(
         workspace_id=workspace.id, user_id=user.id, time_created=created_at, valid=True