Addressed hold type and stale test fixture comments

Author: Nabi

src/types/onyx/Transaction.ts

@@ -64,7 +64,7 @@ type Comment = {
     comment?: string;
 
     /** Whether the transaction is on hold */
-    hold?: string | null;
+    hold?: string;
 
     /** Collection of waypoints associated with the transaction */
     waypoints?: WaypointCollection;

tests/unit/TransactionTest.ts

@@ -1817,7 +1817,7 @@ describe('Transaction', () => {
                             owner: 123,
                         },
                     },
-                    hold: null,
+                    hold: undefined,
                 },
             } as Transaction;