Wrap std::env::set_current_dir

[jplatte]

Idk what the path for this inside fs-err would be, but it can fail if the provided path doesn't exist (and likely also when it's not a directory).

If https://github.com/andrewhickman/fs-err/issues/67 was implemented, this would no longer really be necessary, side-stepping the import path issue.

[schneems]

Do we have a list of functions that produce a std::io::Error that operate on the filesystem that don't have an fs-err wrapper?