Update data-tests.md. Solving double negative. (#4891)

Hi.
Since the tests looks for negative amount records, why not say so
instead of using a double negative, which is not the easiest to read and
involves longer code? Regards.
IL.

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website/docs/docs/build/data-tests.md

@@ -43,13 +43,13 @@ These tests are defined in `.sql` files, typically in your `tests` directory (as
 
 ```sql
 -- Refunds have a negative amount, so the total amount should always be >= 0.
--- Therefore return records where this isn't true to make the test fail
+-- Therefore return records where total_amount < 0 to make the test fail.
 select
     order_id,
     sum(amount) as total_amount
 from {{ ref('fct_payments' )}}
 group by 1
-having not(total_amount >= 0)
+having total_amount < 0
 ```
 
 </File>