gh-119180: Document the format parameter in typing.get_type_hints()

[Viicos]

I'm wondering if we should also update this section:

cpython/Doc/library/typing.rst

Lines 3336 to 3337 in 66e1399

	This is often the same as ``obj.__annotations__``, but this function makes
	the following changes to the annotations dictionary:

This gives some sense that accessing __annotations__ is safe, which is no longer the case.

• Issue: Implement PEP 649 and PEP 749 #119180

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