node12 is deprecated

[badabing2005]

Thanks for the action,

Getting this:
The following actions uses node12 which is deprecated and will be forced to run on node16: skymatic/code-sign-action@v1. For more info: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/

As a side note, it would be handy to be able to specify a file similar to folder, useful where a folder contains multiple signable files but only one is needed to be signed (perhaps best way would be using a filter)