Update SUMMARY.md to correct Extension Manifest entry in the Extensions Overview

Author: Luuk Peters

16/umbraco-cms/SUMMARY.md

@@ -153,8 +153,8 @@
   * [Vite Package Setup](customizing/development-flow/vite-package-setup.md)
 * [Extensions Overview](customizing/extending-overview/README.md)
   * [Extension Registry](customizing/extending-overview/extension-registry/README.md)
+    * [Extension Manifest introduction](customizing/extending-overview/extension-registry/extension-manifest.md)
     * [Register an Extension](customizing/extending-overview/extension-registry/register-extensions.md)
-    * [Extension Manifest](customizing/extending-overview/extension-registry/extension-manifest.md)
     * [Replace, Exclude or Unregister](customizing/extending-overview/extension-registry/replace-exclude-or-unregister.md)
   * [Extension Types](customizing/extending-overview/extension-types/README.md)
     * [App Entry Point](customizing/extending-overview/extension-types/app-entry-point.md)