Fix alias code example for data_tests (#5842)

resolves #5802


[Preview](https://docs-getdbt-com-git-dbeatty10-patch-1-dbt-labs.vercel.app/reference/resource-configs/alias)
(click the "Tests" tab)

## What are you changing in this pull request and why?

Fix the code example.

### 🎩 

Before:

<img width="400" alt="image"
src="https://github.com/user-attachments/assets/5672df92-b004-4125-8311-fa7ca75b3eb0">

After:

<img width="400" alt="image"
src="https://github.com/user-attachments/assets/2146c149-5533-4d0d-a1ce-78e43583cb9e">

## Checklist
- [x] Review the [Content style
guide](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/content-style-guide.md)
so my content adheres to these guidelines.

website/docs/reference/resource-configs/alias.md

@@ -96,8 +96,8 @@ models:
     columns:
       - name: order_id
         tests:
-          - unique
-            alias: unique_order_id_test
+          - unique:
+              alias: unique_order_id_test
 ```
 
 When using `--store-failures`, this would return the name `analytics.finance.orders_order_id_unique_order_id_test` in the database.