This was on oversight on my part: I assumed that the --work-tree arg was
always intended for use with linked worktrees which have a .git file
pointing back to the repo.
I'm honestly confused now: seems like there are three kinds of worktrees:
* the main worktree of a non-bare repo
* a linked worktree (with its own gitdir in the repo's worktrees/ dir)
* a random folder which you specify as a worktree with the --work-tree arg
I'm pretty sure the --work-tree arg is only intended to be used with this
third kind or workree
Afero is a package that lets you mock out a filesystem with an in-memory filesystem.
It allows us to easily create the files required for a given test without worrying about
a cleanup step or different tests tripping on eachother when run in parallel.
Later on I'll standardise on using afero over the vanilla os package
There are quite a few paths you might want to get e.g. the repo's path, the worktree's path,
the repo's git dir path, the worktree's git dir path. I want these all obtained once and
then used when needed rather than having to have IO whenever we need them. This is not so
much about reducing time spent on IO as it is about not having to care about errors every time
we want a path.
Older versions of git don't support the -z flag in `git worktree list`.
So we're using newlines.
Also, we're not raising an error upon error because that triggers another refresh,
which gets us into an infinite loop
