[Typescript] Fix props not spreadable to input elements

[mwszekely]

This is meant to be an extremely minor fix for the following problem I've run into in the most recent version of Preact:

// Props are spreadable to all types except for input elements
const a = <div {...({} as h.JSX.HTMLAttributes<HTMLDivElement>)} />;            // Works fine
const b = <input {...({} as h.JSX.HTMLAttributes<HTMLInputElement>)} />;        // TS Error

The only change was updating its definition from

input: HTMLAttributes<HTMLInputElement> & { defaultValue?: string };

to

input: HTMLAttributes<HTMLInputElement> & { defaultValue?: string | SignalLike<string> };

I will admit I'm not sure if there's a deeper issue that was causing the problem or if this has unintended consequences elsewhere, but just adjusting this one single type seemed to solve everything that I had noticed personally.

[coveralls]

Coverage remained the same at 99.53% when pulling b99d217 on mwszekely:master into 43204de on preactjs:master.