Switch upload-release-asset to maintained version

[bovine3dom]

The one we're using has been archived and is using save-state stuff that will be removed soon

https://github.com/softprops/action-gh-release

Could maybe be a good idea to combine the release/compile workflows into one using https://github.com/softprops/action-gh-release#user-content--limit-releases-to-pushes-to-tags

Edit: maybe worth forking this repo so that we're not messing around doing real releases when we're trying to work out how it works