Fix column defaults test for MySQL

MySQL does not delete any rows without a where clause.

tests/test_databases.py

@@ -951,7 +951,9 @@ async def test_column_defaults(database_url):
             await database.execute(query)
             results = await database.fetch_all(query=timestamps.select())
             assert len(results) == 1
-            await database.execute(timestamps.delete())
+            await database.execute(
+                timestamps.delete(timestamps.c.id == results[0]["id"])
+            )
 
             # with default value overridden
             dt = datetime.datetime.now() - datetime.timedelta(seconds=10)