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' }]
}