Tienes que ser la única persona en el mundo a la que no le gusta que la asciendan.

- You must be the only person in the world that doesn't like to be promoted.

Why isn't gustar in the subjunctive tense here? It is a subjective statement to say that someone must be the only person in the world. Here is a counter-example (where enterarse is in the subjunctive):
- Los chismes, que todo el mundo se entere cuando rompiste con tu novio…
- The gossips, that everyone would find out when you broke up with your boyfriend...

Here it is in the subjunctive since it is likewise speculative to say that everyone would find out something.

My guess is that this sentence is not speculative or that the author wants to make it sound like a statement of fact.