test 106_02: also allow error 56

Author: icing

test/modules/http2/test_106_shutdown.py

@@ -66,7 +66,7 @@ def test_h2_106_02(self, env):
             r = env.curl_get(url, options=['-v'])
             # requests should succeed, but rarely connections get closed
             # before the response is received
-            if r.exit_code in [16, 55]:
+            if r.exit_code in [16, 55, 56]:
                 # curl send error
                 assert r.response is None
             else: