chore: fix version replacement regex in test

We're now on Svelte v5.0.0-next.42 which made one test match the 42 of the next version instead of the number in the code, resulting in that test suddenly failing. This fixes the regex to replace that number with x's instead

Author: dummdidumm

packages/svelte/tests/sourcemaps/test.ts

@@ -50,7 +50,7 @@ const { test, run } = suite<SourcemapTest>(async (config, cwd) => {
 		css = { code: '', map: /** @type {any} */ null };
 	}
 
-	js.code = js.code.replace(/generated by Svelte v\d+\.\d+\.\d+/, (match) =>
+	js.code = js.code.replace(/\(Svelte v\d+\.\d+\.\d+(-next\.\d+)?/, (match) =>
 		match.replace(/\d/g, 'x')
 	);