Object.groupBy types are wrong (remove Partial<>) #1943

const grouped = Object.groupBy(
  [
      {
          name: "foo",
          value: 20,
      },
      {
          name: "bar",
          value: 60,
      },
      {
          name: "bar",
          value: 40,
      }
  ],
  ({name}) => name,
);
for (const group of Object.values(grouped)) {
  group.forEach(console.log)
  // 'group' is possibly 'undefined'.(18048)
}