fix: check winboat disk space instead of its parent path

[GetPsyched]

Fixes #404

I personally don't like this approach as this breaks general expectations I'd have as a user. I better like (with bias) the approach I suggested here.

Marking this as draft until there's more discussion on the tracking issue.

[waffles-dev]

My suggestion in #404 was purely because it didn't fundamentally change the intent of that check. I'm not wed to the suggestion - happy to change intent if Tibix or Levev approve.