Support only formatting changed files

[Riley19280]

When setting up this action, I expected the onlyDirty: true argument to only format changed files in the PR, since this is a fairly common use case for linting. However, it did not format anything, because all changes are already committed, and that is how Pint works.

I propose adding an option onlyChanged that would only format the files changed in the PR/commit. This was referenced in #5 (comment), and a workaround was given, to use another action to format only changed files. However, using the get all changed files action, I don't see any way that I would pass a list of files to format to Pint.

[aglipanci]

@Riley19280 you are welcome to create a PR for this, it's not on my plans to work on this feature in particular anytime soon.

[sergotail]

@Riley19280 i've implemented the same action, but tried to address issues of current package, maybe it will help: https://github.com/sergotail/laravel-pint-action