Warning when running PR tests: wrapping `Vararg` directly in UnionAll is deprecated

The following warning is generated:
```
┌ BeamTracking
│ 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)`.
└
```

Start by running the PR test suite to reproduce the deprecation warning, then search the repository for direct Vararg usage and the BeamTracking code path that emits it. Done means the warning no longer appears during the PR tests without changing their intended behavior.

Written by the indexing model from the issue text.