chore(deps): update dependency sinon to v21 (spectrum-two)

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
sinon (source)	^20.0.0 -> ^21.0.0

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Release Notes

sinonjs/sinon (sinon)

v21.0.0

Compare Source

• fd10f13f
  chore!: remove assert.failException property (#​2659) (Morgan Roderick)

  This was used for allowing customisation of the thrown error between
  sandboxes and for customisation for integrations (most likely from the
  days of BusterJS).

  To my knowledge and what I've been able to find on GitHub, this has
  never had any production use by end users.

  BREAKING CHANGE: this removes assert.failException from the API

Released by Morgan Roderick on 2025-06-13.

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[castastrophe]

Nothing in this breaking change impacts our use of the tool and the plugin tests continue to pass in CI.