Fix TypeError in test_db.py, which did't expect alembic.ini param

...
        config = pretend.stub(
            registry=pretend.stub(settings={"database.url": pretend.stub()})
        )

>       alembic_config = _configure_alembic(config)

tests/unit/test_db.py:97:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

config = <stub(registry=<stub(settings={'database.url': <stub()>})>)>

    def _configure_alembic(config):
>       alembic_cfg = alembic.config.Config("warehouse/migrations/alembic.ini")
E       TypeError: config_cls() takes 0 positional arguments but 1 was given

Author: abitrolly

tests/unit/test_db.py

@@ -85,7 +85,7 @@ def handler(config):
 def test_configure_alembic(monkeypatch):
     config_obj = pretend.stub(set_main_option=pretend.call_recorder(lambda *a: None))
 
-    def config_cls():
+    def config_cls(file_=None):
         return config_obj
 
     monkeypatch.setattr(alembic.config, "Config", config_cls)