Returned REGISTRY_KEYS for import, after was drop in recent merges

src/scvi/model/base/_archesmixin.py

@@ -12,7 +12,7 @@
 from mudata import MuData
 from scipy.sparse import csr_matrix
 
-from scvi import settings
+from scvi import REGISTRY_KEYS, settings
 from scvi._types import AnnOrMuData
 from scvi.data import _constants
 from scvi.data._constants import _MODEL_NAME_KEY, _SETUP_ARGS_KEY, _SETUP_METHOD_NAME