Fix suggested alternative for deprecated Claude Sonnet 3.5

[AlexanderMelde]

Code of Conduct

• I have read and agree to the GitHub Docs project's Code of Conduct

What article on docs.github.com is affected?

https://docs.github.com/en/copilot/reference/ai-models/supported-models

What part(s) of the article would you like to see updated?

In the current version of the documentation, a deprecated model's alternative is referencing to itself.

Additional information

No response

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