No wrapping Vararg in UnionAll

[KnutAM]

Was missed in #872, not sure how this could be tested to catch...?

https://github.com/JuliaLang/julia/blob/3a3289a17f5a36feddf0898b67788b894a5c7440/src/jltypes.c#L919-L920

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.25%. Comparing base (f245839) to head (9c9c717).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1285   +/-   ##
=======================================
  Coverage   94.25%   94.25%           
=======================================
  Files          40       40           
  Lines        6750     6750           
=======================================
  Hits         6362     6362           
  Misses        388      388           

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[KnutAM]

Fixes the following warning during precompilation

Precompiling packages finished.
  5 dependencies successfully precompiled in 11 seconds. 166 already precompiled.
  1 dependency had output during precompilation:
┌ Ferrite
│  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)`.
│  To make this warning an error, and hence obtain a stack trace, use `julia --depwarn=error`.
└  

[KristofferC]

I'm not sure this really need to be tested

[KnutAM]

I'm not sure this really need to be tested

I was thinking in general if there was an easy test using deprecated syntax etc. occurring during precompilation could be caught. But agreed that it is not crucial.