* Says not worried about future of HK as global financial hot spot. : SINGAPORE (Reuters) - Singapore sovereign wealth fund GIC Pte Ltd said it is now more cautious about the investing environment than it was last year and is bracing for low returns due to high valuations and slowing economic growth. But while GIC, among the world’s biggest investors, is worried about heightened political and policy uncertainty, including the Sino-U.S. trade war, it is positioning itself to cushion the impact by investing in countries such as Vietnam which are benefiting from a shift in supply chains.