test: fix flaky test-domain-timers

It's possible for this test to be extremely infrequently flaky if
1ms or more elapses between setting the two timeouts. In that case,
the second timer will not fire and the test will fail.

PR-URL: https://github.com/nodejs/node/pull/21019
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

test/parallel/test-domain-timers.js

@@ -28,7 +28,6 @@ const timeoutd = domain.create();
 
 timeoutd.on('error', common.mustCall(function(e) {
   assert.strictEqual(e.message, 'Timeout UNREFd');
-  clearTimeout(timeout);
 }, 2));
 
 let t;
@@ -38,6 +37,7 @@ timeoutd.run(function() {
   }, 0).unref();
 
   t = setTimeout(function() {
+    clearTimeout(timeout);
     throw new Error('Timeout UNREFd');
   }, 0);
 });