doc: update name of Node.js core Slack channel

The name has been changed from nodejs-dev to nodejs-core.

PR-URL: https://github.com/nodejs/node/pull/45293
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

doc/contributing/pull-requests.md

@@ -47,7 +47,7 @@ Node.js has many channels on the
 channels are:
 [#nodejs](https://openjs-foundation.slack.com/archives/CK9Q4MB53) for general
 help, questions, and discussions.
-[#nodejs-dev](https://openjs-foundation.slack.com/archives/C019Y2T6STH) for
+[#nodejs-core](https://openjs-foundation.slack.com/archives/C019Y2T6STH) for
 development of Node.js core specifically.
 
 Node.js also has an unofficial IRC channel:

onboarding.md

@@ -58,7 +58,7 @@ onboarding session.
 
 The project has a venue for real-time discussion:
 
-* [`#nodejs-dev`](https://openjs-foundation.slack.com/archives/C019Y2T6STH) on
+* [`#nodejs-core`](https://openjs-foundation.slack.com/archives/C019Y2T6STH) on
   the [OpenJS Foundation Slack](https://slack-invite.openjsf.org/)
 
 ## Project goals and values