New comment by Duncaen on void-packages repository

https://github.com/void-linux/void-packages/pull/30147#issuecomment-819059515

Comment:
Probably a good idea to use `$XBPS_REPOSITORY`, instead of `$XBPS_HOSTDIR/binpklgs`, then it would act the same way as other xbps-src commands that use repositories.
Would be more predictable for cleaning up branch repositories and would allow to switch to different repos with `-r`.