gh-120384: Fix array-out-of-bounds crash in list_ass_subscript (#120442)

Lib/test/test_list.py

@@ -245,6 +245,20 @@ class ListTest(list_tests.CommonTest):
         with self.assertRaises(TypeError):
             a[0] < a
 
+    def test_list_index_modifing_operand(self):
+        # See gh-120384
+        class evil:
+            def __init__(self, lst):
+                self.lst = lst
+            def __iter__(self):
+                yield from self.lst
+                self.lst.clear()
+
+        lst = list(range(5))
+        operand = evil(lst)
+        with self.assertRaises(ValueError):
+            lst[::-1] = operand
+
     @cpython_only
     def test_preallocation(self):
         iterable = [0] * 10