Export DitheringAlgorithm type from Astro package

.changeset/goofy-trains-joke.md

@@ -0,0 +1,9 @@
+---
+"@sweetcorn/astro": minor
+---
+
+Exports a type to help with typing code that interfaces with the `dither` prop:
+
+```ts
+import type { DitheringAlgorithm } from '@astrojs/sweetcorn`;
+```

packages/astro/index.ts

@@ -3,6 +3,8 @@
 import type { AstroIntegration } from 'astro';
 import type { SweetcornImageConfig } from './types';
 
+export type DitheringAlgorithm = Exclude<Astro.CustomImageProps['dither'], false | undefined>;
+
 export default function sweetcornAstro<T extends string = never, D extends string = never>(
 	config: SweetcornImageConfig<T, D> = {}
 ) {