test: allow numeric string for lookupService test

Fixes: nodejs#42164

If the given port number isn't associated with any service name,
the `service` resolved from `dns.lookupService` can be a numeric
string representing the port number.

PR-URL: nodejs#42596
Reviewed-By: Mohammed Keyvanzadeh <mohammadkeyvanzade94@gmail.com>
Reviewed-By: Akhil Marsonya <akhil.marsonya27@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>

test/parallel/test-dns-lookupService-promises.js

@@ -6,7 +6,7 @@ const assert = require('assert');
 const dnsPromises = require('dns').promises;
 
 dnsPromises.lookupService('127.0.0.1', 22).then(common.mustCall((result) => {
-  assert.strictEqual(result.service, 'ssh');
+  assert(['ssh', '22'].includes(result.service));
   assert.strictEqual(typeof result.hostname, 'string');
   assert.notStrictEqual(result.hostname.length, 0);
 }));