Update billing docs: failed executions are now charged (#795)

* Update billing docs: failed executions are now charged

* Update billing.mdx

Author: karimhass

api-reference/overview/billing.mdx

@@ -6,7 +6,7 @@ icon: "file-invoice-dollar"
 Pricing for API is charged along two dimensions. All details can be found at [dune.com/pricing](https://dune.com/pricing)
 
 <Note>
-If your execution fails, then no credits are charged. If you execute a query but never pull the results, you are only charged for the execution.
+Failed executions are charged. If you execute a query but never pull the results, you are only charged for the execution.
 </Note>
 
 | Dimension | Charge |