doc: update guide for assert team

Update the Collaborator Guide to use the assert team for notifications
on assert module issues and pull requests.

PR-URL: #23085
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

Author: Trott

COLLABORATOR_GUIDE.md

@@ -853,7 +853,7 @@ LTS working group and the Release team.
 | ---                                      | ---                                                                   |
 | `benchmark/*`                            | @nodejs/benchmarking, @mscdex                                         |
 | `doc/*`, `*.md`                          | @nodejs/documentation                                                 |
-| `lib/assert`                             | @nodejs/testing                                                       |
+| `lib/assert`                             | @nodejs/assert                                                        |
 | `lib/async_hooks`                        | @nodejs/async\_hooks for bugs/reviews (+ @nodejs/diagnostics for API) |
 | `lib/buffer`                             | @nodejs/buffer                                                        |
 | `lib/child_process`                      | @nodejs/child\_process                                                |