Fix typo in dangerfile.js which results in an unreachable code path… (#32277)

## Summary Fix typo in dangerfile.js which results in an unreachable code path which ought to be hit when there is no matching base artifact during DangerCI automated code review. See: https://github.com/facebook/react/blob/221f3002caa2314cba0a62950da6fb92b453d1d0/dangerfile.js#L73 Compare: https://github.com/facebook/react/blob/221f3002caa2314cba0a62950da6fb92b453d1d0/dangerfile.js#L171 And the case which should hit this code path: https://github.com/facebook/react/blob/221f3002caa2314cba0a62950da6fb92b453d1d0/dangerfile.js#L160 Given the above context, the condition `Number === Infinity` is clearly meant to be `decimal === Infinity`, which it will be if the `catch` statement triggers when there is no matching base artifact. Without this fix, the primitive value `Infinity` is passed to `percentFormatter.format(decimal)`, resulting in the string `'+∞%'`. With this fix, the resulting string will be the intended `'New file'`. ## [Resolves issue 32278](https://github.com/facebook/react/issues/32278)