docs: fix openapi yaml lint (#6948)

saw this in the super lint.

rpc/openapi/openapi.yaml

@@ -607,11 +607,12 @@ paths:
       operationId: unsafe_flush_mempool
       tags:
         - Unsafe
-      description: 
+      description: |
         Flush flushes out the mempool. It acquires a read-lock, fetches all the
         transactions currently in the transaction store and removes each transaction
         from the store and all indexes and finally resets the cache.
-        NOTE: Flushing the mempool may leave the mempool in an inconsistent state.
+
+        Note, flushing the mempool may leave the mempool in an inconsistent state.
       responses:
         "200":
           description: empty answer