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

[github-actions[bot]]

Package name	latest	stable
MeasureTheory.jl

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (609a2bd) 55.55% compared to head (d745078) 55.55%.

Additional details and impacted files

@@           Coverage Diff           @@
##           mt-015     #123   +/-   ##
=======================================
  Coverage   55.55%   55.55%           
=======================================
  Files          42       42           
  Lines        1179     1179           
=======================================
  Hits          655      655           
  Misses        524      524           

Files Changed	Coverage Δ
src/combinators/smart-constructors.jl	24.69% <ø> (ø)
src/combinators/power.jl	82.25% <100.00%> (ø)
src/static.jl	80.00% <100.00%> (ø)

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[oschulz]

I have this in #122 already, I think - if it's ok I'd hold off until that done (hopefully very soon) to reduce merge conflicts.

[cscherrer]

I don't think so, the pr targets that branch

[cscherrer]

OTOH no problem waiting if you prefer, it's pretty minor I think

[oschulz]

Thanks - I'll get back to that monster-PR, promise!

[oschulz]

Included in #142