fix: update flat files setup to support multisite mode

Author: imantsk

tests/e2e/flat-files.setup.ts

@@ -1,7 +1,9 @@
 import { expect, test as setup } from '@playwright/test'
 
 setup('enable flat files', async ({ page }) => {
-	await page.goto('/wp-admin/admin.php?page=snippets-settings')
+	const wpAdminbase = process.env.WP_E2E_MULTISITE_MODE ? '/wp-admin' : '/wp-admin/network'
+  
+	await page.goto(`${wpAdminbase}/admin.php?page=snippets-settings`)
 	await page.waitForSelector('#wpbody-content')
 
 	await page.waitForSelector('form')