Fix TF Bots firing at enemy players while a truce is active

[WereTech]

Currently, TF Bots will continue firing at enemy players during a truce, resulting in uselessly firing at the enemy as they cannot be damaged. This adds an override to INextBot's IsEnemy to now check if a truce is active, and if so, ignore players that are on both Blue and Red team as bosses should be on a separate team.