Update permissions from 777 to 1777 (redux)

I somehow missed Debian in 25b3034 (only updated Alpine), so this updates Debian in the same way.

> This still supports the "arbitrary user" use case but with slightly tighter permissions on the end result.
>
> This one is a little bit more "special" other images (due to the existing runtime/entrypoint modification of the directory modes) so I've tried to pick reasonable values for both halves.

Author: tianon