"Goes" implies movement, Ray Ray, so I wouldn't use it before "unchanging" because those words seem somewhat contradictory to me.
I'd probably say that the trend doesn't change. "Remains/stays unchanging" seems okay to me if you want to emphasize that the trend does not change for some length of time.
It would be useful to know if the trend is f(x), f(nx) or f(xn) but to me, goes, stays, and unchanging are not particularly idiomatic when describing a trend in a graph.
