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: #21019
Reviewed-By: Michael Dawson <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Weijia Wang <[email protected]>
Reviewed-By: Daniel Bevenius <[email protected]>

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);
 });