noexec mount option not working in Debian 9 installer

[Augustus Johnson <augustus0008@gmail.com>]

Hi,

I had set the noexec mount option on /tmp while installing Debian 9
using firmware-9.5.0-amd64-DVD-1.iso.

But after the installation was completed, the mount option was found
missing.  This same behaviour is noticed when installing the OS using
preseed.

root@mountoptions:~# mount | grep /tmp
/dev/sda5 on /tmp type ext4 (rw,nosuid,nodev,relatime,data=ordered)

Thanks,
Augustus.