Before, we bind-mounted /dev/ptmx and /dev/pts from the host into the
chroot. This will make posix_openpt() fail with 'No such file or
directory'. The ability to create pseudo terminals is important for apt
(which will throw a warning otherwise) or running script(1) or source
package testsuites like for src:util-linux. This functionality is
restored by mounting a new devpts instance to /dev/pts and making
/dev/ptmx a symlink to /dev/pts/ptmx. Mounting with ptmxmode=666 is
required such that also non-root users in unshare mode are able to
create pseudo terminals. See also:
https://www.kernel.org/doc/Documentation/filesystems/devpts.txthttps://salsa.debian.org/debian/schroot/-/merge_requests/2https://bugs.debian.org/856877https://bugs.debian.org/817236
