mpy: prevent garbage collection from closing stdin

Somwhere in Micropython there's a `<io.TextIOWrapper 0>` from
vfs_posix_file that's getting garbage collected and which in turn
triggers the object's __del__ which then in turn attempt to close FD 0.

Let's not allow that to happen by adding some ugly hardcoded deny list
for FD 0,1,2 in the close function.

Ideally, we would figure out why that object exists, why it gets garbage
collect and what really should happen here. But this is good enough.