docs(config): fix type of preview.allowedHosts to 'string[] | true' (#20688)

Author: wo-o29

docs/config/preview-options.md

@@ -21,7 +21,7 @@ See [`server.host`](./server-options#server-host) for more details.
 
 ## preview.allowedHosts
 
-- **Type:** `string | true`
+- **Type:** `string[] | true`
 - **Default:** [`server.allowedHosts`](./server-options#server-allowedhosts)
 
 The hostnames that Vite is allowed to respond to.