Update insertSiblings type definition

[samends]

Type: Bug

The following has been addressed in the PR:

• There is a related issue
• All code has been formatted with prettier as per the readme code style guidelines
• Unit or Functional tests are included in the PR

Description:

Resolves #870
Updates type definitions for insertSiblings function

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[codecov]

Codecov Report

Merging #872 (44e0ce9) into master (9bbcff9) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #872   +/-   ##
=======================================
  Coverage   94.72%   94.72%           
=======================================
  Files         127      127           
  Lines        8130     8130           
  Branches     1894     1894           
=======================================
  Hits         7701     7701           
  Misses        429      429           

Impacted Files	Coverage Δ
src/testing/renderer.ts	97.32% <ø> (ø)

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[agubler]

@samends I think we can add a test that uses this API with a function based widget - without your changes it should fail with compilation errors and after should work?

[samends]

Make sense, I'll add that in