Method downgrade

crates/vm/src/object/core.rs:1389–1395

(
        &self,
        callback: Option<PyObjectRef>,
        vm: &VirtualMachine,
    )

    }

    pub fn downgrade(
        &self,
        callback: Option<PyObjectRef>,
        vm: &VirtualMachine,
    ) -> PyResult<PyRef<PyWeak>> {
        self.downgrade_with_typ(callback, vm.ctx.types.weakref_type.to_owned(), vm)
    }

    pub fn get_weak_references(&self) -> Option<Vec<PyRef<PyWeak>>> {
        self.weak_ref_list()