chore: update README.md asset URL (#9104)

Updated README asset URL

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### What?
Update README asset URL for hero

### Why?
Reflect latest Payload branding

### How?
URL change for correct asset

-->

README.md

@@ -1,4 +1,4 @@
-<a href="https://payloadcms.com"><img width="100%" src="https://github.com/payloadcms/payload/blob/main/packages/payload/src/admin/assets/images/github-banner-nextjs-native.jpg?raw=true" alt="Payload headless CMS Admin panel built with React" /></a>
+<a href="https://payloadcms.com"><img width="100%" src="https://github.com/payloadcms/payload/blob/beta/packages/payload/src/assets/images/github-banner-nextjs-native.jpg" alt="Payload headless CMS Admin panel built with React" /></a>
 <br />
 <br />