debugger: indicate server is ending

Currently, we say "listening" when we are ending the server. Change it
to "ending".

Fixes: https://github.com/nodejs/node/issues/39272

PR-URL: https://github.com/nodejs/node/pull/39334


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Yash Ladha <yash@yashladha.in>