fix(rss): use node assert instead of chai (withastro#9980)

packages/astro-rss/test/rss.test.js

@@ -240,25 +240,30 @@ describe('getRssString', () => {
 	});
 
 	it('should not fail when an enclosure has a length of 0', async () => {
-		const str = await getRssString({
-			title,
-			description,
-			items: [
-				{
-					title: 'Title',
-					pubDate: new Date().toISOString(),
-					description: 'Description',
-					link: '/link',
-					enclosure: {
-						url: '/enclosure',
-						length: 0,
-						type: 'audio/mpeg',
+		let error = null;
+		try {
+			await getRssString({
+				title,
+				description,
+				items: [
+					{
+						title: 'Title',
+						pubDate: new Date().toISOString(),
+						description: 'Description',
+						link: '/link',
+						enclosure: {
+							url: '/enclosure',
+							length: 0,
+							type: 'audio/mpeg',
+						},
 					},
-				},
-			],
-			site,
-		});
+				],
+				site,
+			});
+		} catch (e) {
+			error = e.message;
+		}
 
-		chai.expect(str).to.not.throw;
+		assert.strictEqual(error, null);
 	});
 });