Test directly looks to see if a I:S:A.listen returns a usable Tap

This is an improved test for:
      rakudo/rakudo#2411

S32-io/IO-Socket-Async.t

@@ -298,8 +298,8 @@ for '127.0.0.1', '::1' -> $host {
     my $listen-socket = IO::Socket::Async.listen("127.0.0.1", 0);
     react {
         my $listen-tap = do whenever $listen-socket -> $socket { … }
-        lives-ok { await $listen-tap.socket-port }, "can await on socket-port";
-        ok $listen-tap.socket-port.result > 0, "port looks reasonable";
+        ok $listen-tap.defined, "listen tap is defined";
+        isa-ok $listen-tap, Tap, "listen tap is a Tap";
         done;
     }
 }