Create a PR check for default values in action.yml

[febuiles]

Recent changes inadvertently broke the external configuration capabilities of our Action by introducing default values in action.yml, as detailed in this pull request.

It's clear that merely commenting at the top of a file isn't sufficient to prevent these issues. To address this, I suggest implementing a check for every pull request that edits action.yml to ensure no new default values are added, except for the token. We can achieve this with either an NPM script or a shell command.