hub: specify branch so old checkouts aren't broken

Fixes #33437.
This is just a small program forked from https://github.com/selkhateeb/hardlink which creates hardlinks between folders which are otherwise not possible. The name of the formula doesn't match the binary (hln vs hardlink-osx) because the name hardlink was taken!

The code if very straightforward and commented well. I believe this formula should have the
name "hardlink" because it is more accurate than the current one.
hardlink-osx: add 0.3 bottle.