interp: reenable pty test on Mac on CI
interp: reenable pty test on Mac on CI

It's been a year, and the library and Mac environment have both changed.

If the error pops up again, at least now I understand PTYs a bit better.

While at it, use more consistent naming for pty vs tty.

See #513.

mvdan/sh,mvdan/sh,mvdan/sh,mvdan/sh