Prevent uploading UNRELEASED commits

If debian/changelog says UNRELEASED the pipeline does a non-release build by appending a git short hash to the source package version and by not committing to the pristine-lfs branch nor adding the version tag.

However, if the commit gets landed to an $OSNAME/* branch the non-release source gets uploaded to the actual main OBS project, inevitably causing confusion.

Fail hard if we detect that case, rather than just printing a warning.