“Cannot resolve forward reference” when using a type variable defined by Python 3.12 type syntax

[flying-sheep]

class Foo[T]:
   def __init__(self, thing: T) -> None: pass

will result in sphinx.errors.SphinxWarning: Cannot resolve forward reference in type annotations of "mylib.Foo": name 'T' is not defined

This should not be the case, as the [T] syntax defines it. See type parameter lists/
PEP 696