test: fix flaky test-gc-net-timeout

If the timeout is called in the time between 'end' and 'close'
that would cause a EPIPE error. Essentially making the test flaky.

PR-URL: nodejs#31918
Reviewed-By: Anna Henningsen <anna@addaleax.net>

test/parallel/test-gc-net-timeout.js

@@ -12,6 +12,9 @@ function serverHandler(sock) {
   sock.on('close', function() {
     clearTimeout(timer);
   });
+  sock.on('end', function() {
+    clearTimeout(timer);
+  });
   sock.on('error', function(err) {
     assert.strictEqual(err.code, 'ECONNRESET');
   });