fix compiler docs titles

packages/svelte/scripts/process-messages/index.js

@@ -71,13 +71,17 @@ function run() {
 			);
 		}
 
+		// compile errors and warnings don't have sub-categories so they must use the
+		// h2 notation to correctly display in the 'On this page' list of the docs site
+		const heading_notation = category.startsWith('compile-') ? '##' : '###';
+
 		fs.writeFileSync(
 			`${DIR}/${category}.md`,
 			'<!-- This file is generated by scripts/process-messages/index.js. Do not edit! -->\n\n' +
 				Object.entries(messages[category])
 					.map(([code, { messages, details }]) => {
 						const chunks = [
-							`### ${code}`,
+							`${heading_notation} ${code}`,
 							...messages.map((message) => '```\n' + message + '\n```')
 						];