Run pyrefly in typeshed CI

[lolpack]

Pyrefly should be integrated into typeshed to detect bugs in new stubs or mismatches as a result of underlying package upgrades.

[lolpack]

Assigning this to @migeed-z

[connernilsen]

Wait @lolpack, what's this issue about? I'm not sure I understand the description

[ndmitchell]

The Typeshed CI should run Pyrefly on commits, in the same way it runs mypy, so we validate that Typeshed always works with Pyrefly.

[github-actions]

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