fix reference to non-existent module

[bzoracler]

This is a minor fix to a reference to a no-longer-existing private module. There should be no runtime effects, because the fix is made under a typing.TYPE_CHECKING block.

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I've read through #7469, where there was a public API typing change

• _pytest.code.ExceptionInfo -> pytest.ExceptionInfo

but as the rest of the references in the same block in _pytest/hookspec.py are all for private modules, I thought it would be best to continue using a private module instead of switching the reference to a public from pytest import ExceptionInfo.

[bluetech]

Thank you!