Fix import for sqlalchemy 1.4

RowProxys no longer exist. We can't change
it to the new Row's because they don't exist
in older sqlachemy.

cubedash/summary/_stores.py

@@ -31,7 +31,7 @@
 from sqlalchemy import DDL, String, and_, func, select, exists, or_, union_all, literal
 from sqlalchemy.dialects import postgresql as postgres
 from sqlalchemy.dialects.postgresql import TSTZRANGE
-from sqlalchemy.engine import Engine, RowProxy
+from sqlalchemy.engine import Engine
 from sqlalchemy.sql import Select
 
 try:
@@ -599,7 +599,7 @@ def _find_product_fixed_metadata(
             product=product.name,
             sample_percentage=round(sample_percentage, 2),
         )
-        result: List[RowProxy] = self._engine.execute(
+        result = self._engine.execute(
             select(
                 [
                     (
@@ -612,7 +612,7 @@ def _find_product_fixed_metadata(
             )
             .select_from(dataset_table)
             .where(dataset_table.c.dataset_type_ref == product.id)
-            .where(dataset_table.c.archived == None)
+            .where(dataset_table.c.archived.is_(None))
         ).fetchall()
         assert len(result) == 1