Workplace Christmas Meal as Employee

AsalaamuAlaikum

If the workplace is holding a meal (with only Halal food and no alcohol and no music) in December near Christmas time, would a Muslim who goes with the intention of daroora in an attemp to stay in the ‘good books’ of the managers become a kafir by going to such a meal or would he just be sinful?

(Please note that the Muslim’s intention of going to the meal is only to be seen by management as a good employee. The intention is not to revere Christianity or to show any kind of appreciation to Christmas)