tools: change commit fetch limiting in find-inactive-collaborators

GitHub Action workflows can be told to clone a certain number of commits
or else everything. Change find-inactive-collaborators to take a number
of commits to examine rather than a date range so that the parameter can
be used in GitHub Actions.

PR-URL: https://github.com/nodejs/node/pull/39362


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>