TypeScript 4.4 support

[younho9]

Could I request upgrade TypeScript compiler v4.4.2?

Currently tsd can't recognize symbol pattern index signature, but tsc can.

// An index signature parameter type must be either string or number.
expectType<{ 
    [x: symbol]: string
  }>({
    [Symbol('one')]: 'one',
    [Symbol('two')]: 'two',
    [Symbol('three')]: 'three',
  });

Also is there any update on this issue? #47

[sindresorhus]

Fixed by #124