Disable keys using (e)logind config
You just need to edit /etc/systemd/logind.conf
if you use logind or /etc/elogind/elogind.conf
if you use elogind (present in some systemd-less distros).
Search these lines:
#HandleSuspendKey=suspend
#HandleHibernateKey=suspend
and replace them by
HandleSuspendKey=no
HandleHibernateKey=no
Now restart your computer and all is now OK!