Don't display `NG` when `decorations = false`

[dpsanders]

julia> setdisplay(decorations = false);

julia> x = 3..Inf
[3.0, ∞)

julia> f(y) = y^2 - 2

julia> f(x)
[7.0, ∞)_NG

[OlivierHnt]

This is the intended behaviour. But it may be worth having an additional option to setdisplay to remove the "NG" flag.