What should I care about?
TL;DR The action input names have been converted to use kebab-case and marked deprecated. But the old names still work.
This is made to align the public API with the de-facto conventions in the ecosystem. We've used snake_case names, which the maintainer considers a historical mistake. New kebab-case inputs will make the end-users' workflows look more consistent and and visually distinguishable from other identifiers one may encounter in YAML.
There is no timeline for removing the old names, but it will happen in v3 or later versions of the action. If the maintainer doesn't forget to do this, that is.
The patch is here: #125.
Full Diff: v1.6.5...v1.7.0