Fix astro check errors on strict typescript, issue #293

src/types.d.ts

@@ -1,5 +1,5 @@
 import type { AstroComponentFactory } from 'astro/runtime/server/index.js';
-import type { HTMLAttributes } from 'astro/types';
+import type { HTMLAttributes, ImageMetadata } from 'astro/types';
 
 export interface Post {
   /** A unique ID number that identifies a post. */
@@ -21,7 +21,7 @@ export interface Post {
   /** Optional summary of post content. */
   excerpt?: string;
   /**  */
-  image?: string;
+  image?: ImageMetadata | string;
 
   /**  */
   category?: string;