Avoid referencing latest in Dockerfile

[georgespalding]

The Dockerfile used to fetch the binary used for the action references latest in all recent versions.

ARG ASSET_URL=https://github.com/srvaroa/labeler/releases/latest/download/action.tar.gz

This is not great because it put the labeler action out of commision for all releases of the action, when the 1.6.2 release failed to create the action.tar.gz file in "latest" downloads location.

[srvaroa]

Yeah I agree with this. It's a leftover from when the action binary was compiled upon run and I kept it to avoid complicating the release process, but at this point it's safer to go that way.

I'll get this fixed soon.

Thanks!

[srvaroa]

Done.