docs: fix generateImageMetadata example to use normal params object

[marjan-ahmed]

What?

Fixes an inconsistency in the v16 upgrade documentation for generateImageMetadata.

Why?

In the “Upgrading to Version 16” guide, the example incorrectly awaited the params object inside generateImageMetadata, implying that it was a Promise.
However, according to the API reference, params is a normal object. This PR updates the example to reflect the correct synchronous usage.

How?

Replaced:

export async function generateImageMetadata({ params }) {
  const { slug } = await params
  return [{ id: '1' }, { id: '2' }]
}

With
```ts
export async function generateImageMetadata({ params }) {
  // params is a normal object
  return [{ id: '1' }, { id: '2' }]
}

[ijjk]

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[dschafer]

Thanks for the quick PR for #85656 !

I do think there are probably some additional changes needed to make sure the documentation flows reasonably here. If generateImageMetadata gets params synchronously in both v15 and v16, we probably just shouldn’t mention it at all in this migration guide, right?

But I’ll defer to the maintainers on that one.

[marjan-ahmed]

You’re right @dschafer both examples are synchronous. I’ve kept generateImageMetadata as is and clarified that only the Image function uses async props.

[icyJoseph]

Thanks for the PR