[tests] Allow 502 Bad Gateway as well in the SecureTransportTest.Tls12 test. (#13610)

The "502 Bad Gateway" error occurs sometimes on the bots.

Maybe we should rename it "502 Bad Bot"?

tests/monotouch-test/Security/SecureTransportTest.cs

@@ -226,7 +226,8 @@ namespace MonoTouchFixtures.Security {
 
 				string s = Encoding.UTF8.GetString (data, 0, (int) processed);
 				// The result apparently depends on where you are: I get a 302, the bots get a 200.
-				Assert.That (s, Does.StartWith ("HTTP/1.0 302 Found").Or.StartWith ("HTTP/1.0 200 OK"), "response");
+				// Also sometimes it fails with 502 Bad Gateway on the bots
+				Assert.That (s, Does.StartWith ("HTTP/1.0 302 Found").Or.StartWith ("HTTP/1.0 200 OK").Or.StartWith ("HTTP/1.0 502 Bad Gateway"), "response");
 			}
 		}
 #endif // !__WATCHOS__