remove explicit Vararg

[palday]

• add entry in NEWS.md
• after opening this PR, add a reference and run docs/NEWS-update.jl to update the cross-references.

Should we release your changes right away? If so, bump the version:

• I've bumped the version appropriately

@dmbates this should hopefully fix the mysterious warning

WARNING: Wrapping `Vararg` directly in UnionAll is deprecated (wrap the tuple instead)

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (564ce23) 95.90% compared to head (d5f5ea8) 95.90%.

❗ Current head d5f5ea8 differs from pull request most recent head dbb5e0e. Consider uploading reports for the commit dbb5e0e to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #680   +/-   ##
=======================================
  Coverage   95.90%   95.90%           
=======================================
  Files          29       29           
  Lines        2732     2732           
=======================================
  Hits         2620     2620           
  Misses        112      112           

Impacted Files	Coverage Δ
src/MixedModels.jl	100.00% <100.00%> (ø)
src/randomeffectsterm.jl	96.51% <100.00%> (ø)

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[dmbates]

Thanks for finding this and for changing the pre-compilation.