[Portal] Fix Unity link (#4876)

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## PR-Codex overview
This PR updates the links in the `page.mdx` file for the Unity SDK to reflect the correct versioning in the URLs.

### Detailed summary
- Updated the link in the text from `/unity/getting-started` to `/unity/v5/getting-started`.
- Changed the `href` attribute of the `ArticleIconCard` component from `/unity/getting-started` to `/unity/v5/getting-started`.

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Author: 0xFirekeeper

apps/portal/src/app/unity/v5/page.mdx

@@ -22,10 +22,10 @@ You can download the latest version of the SDK from our [GitHub releases page](h
 
 ## Get Started
 
-Check out the [getting started](/unity/getting-started) guide to learn how to use the SDK in less than 2 minutes.
+Check out the [getting started](/unity/v5/getting-started) guide to learn how to use the SDK in less than 2 minutes.
 
 <ArticleIconCard
-	href="/unity/getting-started"
+	href="/unity/v5/getting-started"
 	icon={GraduationCap}
 	title="Get started with the Unity SDK"
 />