chore: fix Vite ecosystem CI test (#15516)

This PR fixes our treeshaking tests so that it specifically looks for
`import { dev }`, etc. instead of just "dev". This helps avoid
false-positive test failures due to the component path being injected as
a comment in the build output that includes the export name we're trying
to assert isn't there

See
https://github.com/vitejs/vite-ecosystem-ci/actions/runs/22842250417/job/66257394232#step:7:3065

It also bumps the Vite 8 beta we use in CI to the latest one to catch
this issue. You can see from the test run that it now includes the
source file path in the build output as a comment
https://github.com/sveltejs/kit/actions/runs/22846427091/job/66263863728?pr=15517#step:10:584

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Author: teemingc

packages/kit/test/apps/basics/test/server.test.js

@@ -888,8 +888,7 @@ test.describe('$app/environment', () => {
 			path.join(root, '.svelte-kit/output/server/entries/pages/treeshaking/dev/_page.svelte.js'),
 			'utf-8'
 		);
-		// check that import { dev } from '$app/environment' is treeshaken
-		expect(code).not.toContain('dev');
+		expect(code).not.toContain('not prod');
 	});
 
 	test('treeshakes browser check', async () => {
@@ -902,8 +901,7 @@ test.describe('$app/environment', () => {
 			),
 			'utf-8'
 		);
-		// check that import { browser } from '$app/environment' is treeshaken
-		expect(code).not.toContain('browser');
+		expect(code).not.toMatch('client');
 	});
 });
 

pnpm-workspace.yaml

@@ -59,7 +59,7 @@ catalogs:
     '@sveltejs/vite-plugin-svelte': ^4.0.0
     'vitest>vite': ^6.0.0 # vitest@4 doesn't work with vite@5, vite@7 doesn't work on node18
   vite-beta:
-    vite: ^8.0.0-beta.9
+    vite: ^8.0.0-beta.18
     '@sveltejs/vite-plugin-svelte': ^7.0.0-next.0
   node-18:
     vite: ^6.0.0 # vite7 requires node20