Fixed test that was failing due to TLS 1.3 backport to Java 8.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

jetty-http2/http2-alpn-tests/src/test/java/org/eclipse/jetty/http2/alpn/tests/ALPNNegotiationTest.java

@@ -164,8 +164,15 @@ public class ALPNNegotiationTest extends AbstractALPNTest
                 encrypted.flip();
             }
             assertEquals(21, encrypted.get());
+            // TLS 1.3 may send 2 alerts: "user_canceled" followed by "close_notify".
             encrypted.clear();
-            assertEquals(-1, channel.read(encrypted));
+            read = channel.read(encrypted);
+            if (read > 0)
+            {
+                encrypted.clear();
+                read = channel.read(encrypted);
+            }
+            assertEquals(-1, read);
         }
     }