fix a memleak (#967)

* fix a memleak

* black
diff --git a/tests/test_crypto.py b/tests/test_crypto.py
index 62b1690..265d31e 100644
--- a/tests/test_crypto.py
+++ b/tests/test_crypto.py
@@ -1625,6 +1625,9 @@
         assert exts[1].get_short_name() == b"keyUsage"
         assert exts[1].get_critical() == 0
         assert exts[1].get_data() == b"\x03\x02\x07\x80"
+        # Requesting it a second time should return the same list
+        exts = request.get_extensions()
+        assert len(exts) == 2
 
     def test_add_extensions_wrong_args(self):
         """