fix replace! stack overflow without method overwrite

[JeffBezanson]

No description provided.

[rfourquet]

Actually this is a good fix but to the wrong problem. As I said in the other issue, initially (in initial versions of #22324) we had something like replace!(prednew::Callable, A; count::Integer=typemax(Int)) = _replace!(prednew, A, Int(count)) and specific implementations had to specialize _replace!(::Callable, A::MyContainer, ::Int) (Int instead of Integer to limit the number of compiled functions, and a positional argument for count to work-around the slowness of forwarded keyword arguments). But Milan rightly suggested that it's nicer that implementations just have to specialize the real function replace! directly. So before merging, I updated this so that implementation have to specialize replace!(::Callable, A; count::Integer) or the same with count::Int, which both created the infinite loop reported in #25384 and actually broke slightly the fallback as it was intended, because dispatch on keywords doesn't work! E.g. in master replace!(x->2x, [1, 2]; count=0x1) errors out. So I will close this and open a PR which just gets rid of this too subtle Int vs Integer distinction, and add tests for when !(count isa Int).
(EDIT: and sorry for these bugs/confusion)