Resurrect two buffer tests, converting irepeat() to imul().  Undoes part of r68962.
diff --git a/Lib/test/test_array.py b/Lib/test/test_array.py
index 08c64cb..c8698bb 100755
--- a/Lib/test/test_array.py
+++ b/Lib/test/test_array.py
@@ -725,6 +725,8 @@
         self.assertRaises(BufferError, operator.setitem, a, slice(0, 0), a)
         self.assertRaises(BufferError, operator.delitem, a, 0)
         self.assertRaises(BufferError, operator.delitem, a, slice(0, 1))
+        self.assertRaises(BufferError, operator.imul, a, 2)
+        self.assertRaises(BufferError, operator.imul, a, 0)
 
     def test_weakref(self):
         s = array.array(self.typecode, self.example)