bpo-35504: Fix segfaults and SystemErrors when deleting certain attrs. (GH-11175)

diff --git a/Lib/sqlite3/test/regression.py b/Lib/sqlite3/test/regression.py
index 1c59a3c..865bd88 100644
--- a/Lib/sqlite3/test/regression.py
+++ b/Lib/sqlite3/test/regression.py
@@ -379,6 +379,10 @@
         del ref
         support.gc_collect()
 
+    def CheckDelIsolation_levelSegfault(self):
+        with self.assertRaises(AttributeError):
+            del self.con.isolation_level
+
 
 class UnhashableFunc:
     __hash__ = None