test: fix flaky addons/callback-scope/test-resolve-async

Fixes: #22668
PR-URL: #22664
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: George Adams <george.adams@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

Author: addaleax

test/addons/callback-scope/test-resolve-async.js

@@ -4,7 +4,9 @@ const common = require('../../common');
 const assert = require('assert');
 const { testResolveAsync } = require(`./build/${common.buildType}/binding`);
 
+// Checks that resolving promises from C++ works.
+
 let called = false;
 testResolveAsync().then(() => { called = true; });
 
-setTimeout(() => { assert(called); }, common.platformTimeout(50));
+process.on('beforeExit', () => { assert(called); });