Usage of env over with for action configuration

[Geod24]

When setting up this action, I was surprised to see the configuration passed using env instead of with, as described in https://help.github.com/en/actions/building-actions/metadata-syntax-for-github-actions#inputs
In essence, it seems that the end result would be pretty much the same ("GitHub stores input parameters as environment variables." according to the doc), but the added bonus is that the input parameters can be documented at the action level (in action.yml).

[pascalgn]

I think the reason is that this action was created before GH added the "with" feature to actions. As far as I know, there is no reason to keep "env", so I think it could make sense to migrate the configuration to use "with".

Feel free to provide a PR, if you like! 👍