fix(build): allow unstable repositories to override repo target

This works around the fact that we are currently not auto detecting unstable repository targets while providing a stability layer option on the subcommand. Soften the --repo option rules by allowing unstable repositories to use that flag for building and releasing against the unstable repositories.

This will be replaced in the near future by proper integration of target repository auto-detection that in aware of unstable repositories while providing a unstable stability layer options.

Component: pkgctl build Component: pkgctl release Signed-off-by: Levente Polyak anthraxx@archlinux.org