Update test-selection-examples.md (#4036)

Improperly defined tests for column

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website/docs/reference/node-selection/test-selection-examples.md

@@ -330,8 +330,8 @@ models:
   - name: orders
     columns:
       - name: order_id
-        tests:
         tags: [my_column_tag]
+        tests:
           - unique
 
 ```