git: security bump to version 2.12.3

Fixes CVE-2017-8386 - Git Shell Bypass By Abusing Less

For more details, see:
https://insinuator.net/2017/05/git-shell-bypass-by-abusing-less-cve-2017-8386/
http://www.mail-archive.com/git@vger.kernel.org/msg120982.html



Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>