fix: remove is:raw from rehype-prism plugin (#15297)

Co-authored-by: Florian Lefebvre <contact@florian-lefebvre.dev>

Author: rururux

.changeset/flat-symbols-arrive.md

@@ -0,0 +1,5 @@
+---
+'@astrojs/markdown-remark': patch
+---
+
+Fixes a case where code blocks generated by prism would include the `is:raw` attribute in the final output

packages/markdown/remark/src/rehype-prism.ts

@@ -11,7 +11,7 @@ export const rehypePrism: Plugin<[string[]?], Root> = (excludeLangs) => {
 				let { html, classLanguage } = runHighlighterWithAstro(language, code);
 
 				return Promise.resolve(
-					`<pre class="${classLanguage}" data-language="${language}"><code is:raw class="${classLanguage}">${html}</code></pre>`,
+					`<pre class="${classLanguage}" data-language="${language}"><code class="${classLanguage}">${html}</code></pre>`,
 				);
 			},
 			excludeLangs,

packages/markdown/remark/test/prism.test.js

@@ -0,0 +1,14 @@
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+import { createMarkdownProcessor } from '../dist/index.js';
+
+describe('prism syntax highlighting', () => {
+	it('does not add is:raw to the output', async () => {
+		const processor = await createMarkdownProcessor({
+			syntaxHighlight: 'prism',
+		});
+		const { code } = await processor.render('```\ntest\n```');
+
+		assert.ok(!code.includes('is:raw'));
+	});
+});