fix unable override injected img component (#3785)

Author: dimaMachina

.changeset/real-fishes-double.md

@@ -0,0 +1,5 @@
+---
+'nextra': patch
+---
+
+fix unable override injected `img` component

packages/nextra/src/client/mdx.ts

@@ -13,10 +13,10 @@ const DEFAULT_COMPONENTS = {
 } satisfies MDXComponents
 
 export const useMDXComponents: typeof originalUseMDXComponents = components => {
-  return originalUseMDXComponents({
+  return {
     ...DEFAULT_COMPONENTS,
-    ...components
-  })
+    ...originalUseMDXComponents(components)
+  }
 }
 
 export { MDXProvider } from '@mdx-js/react'