Make this action available on Marketplace

[webknjaz]

This action isn't listed and I've only discovered this action by following a link on another action's page: https://github.com/marketplace/actions/gentoo-repoman#note.

The current action name set @ https://github.com/pkgcore/pkgcheck-action/blob/5a0413f/action.yml#L1 is already taken and there's another action published on the corresponding page: https://github.com/marketplace/actions/pkgcheck.

To publish this one, it's necessary to:

• change that value to something else
• create a GitHub Release and on the creation page, select an option to publish it to the Marketplace, it will require that the org owners sign the Marketplace agreement when publishing for the first time