Function except_t_fmap 

pub fn except_t_fmap<E: 'static, M: FunctorSt, A: 'static, B: 'static>(
    fa: M::Of<Result<A, E>>,
    f: impl Fn(A) -> B + 'static,
) -> M::Of<Result<B, E>>

ExceptT fmap: apply a function to the Ok value.