Fix `Vararg` warnings

[cscherrer]

In Julia 1.10 beta (at least) we get this warning a lot:

│  WARNING: Wrapping `Vararg` directly in UnionAll is deprecated (wrap the tuple instead).
│  You may need to write `f(x::Vararg{T})` rather than `f(x::Vararg{<:T})` or `f(x::Vararg{T}) where T` instead of `f(x::Vararg{T} where T)`.

Here Simeon Schaub suggests that to address this, "Just use Vararg{Number} instead of Vararg{<:Number}". This PR makes this small change