Update reactStrictMode.mdx enabled since 13.5.1 (#70557)

Spent over 2 hours checking why with 13.4.19 components didn't mount
twice as the docs says "Good to know: Since Next.js 13.4, Strict Mode is
true by default with app router".

But it's enabled by default in
[13.5.1](https://github.com/vercel/next.js/releases/tag/v13.5.1).

Version [13.5.0](https://github.com/vercel/next.js/releases/tag/v13.5.0)
has no changelog?

Maybe reactStrictMode it's enabled by default since 13.5.0 instead
13.5.1 ?

Fixes: #70559

Co-authored-by: JJ Kasper <[email protected]>

docs/02-app/02-api-reference/05-next-config-js/reactStrictMode.mdx

@@ -5,7 +5,7 @@ description: The complete Next.js runtime is now Strict Mode-compliant, learn ho
 
 {/* The content of this doc is shared between the app and pages router. You can use the `<PagesOnly>Content</PagesOnly>` component to add content that is specific to the Pages Router. Any shared content should not be wrapped in a component. */}
 
-> **Good to know**: Since Next.js 13.4, Strict Mode is `true` by default with `app` router, so the above configuration is only necessary for `pages`. You can still disable Strict Mode by setting `reactStrictMode: false`.
+> **Good to know**: Since Next.js 13.5.1, Strict Mode is `true` by default with `app` router, so the above configuration is only necessary for `pages`. You can still disable Strict Mode by setting `reactStrictMode: false`.
 
 > **Suggested**: We strongly suggest you enable Strict Mode in your Next.js application to better prepare your application for the future of React.