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!