debugger: revise async iterator usage to comply with lint rules

I'm not sure that this is any clearer than the existing code, but I
don't think it's significantly less clear, and it avoids comment
disabling a lint rule.

PR-URL: https://github.com/nodejs/node/pull/38847


Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>