update error message in test files (#7493)

Signed-off-by: Sally MacFarlane <macfarla.github@gmail.com>

acceptance-tests/tests/src/test/resources/jsonrpc/engine/shanghai/test-cases/05_shanghai_prepare_payload_invalid_null_withdrawals.json

@@ -21,7 +21,7 @@
     "id" : 67,
     "error" : {
       "code" : -32602,
-      "message" : "Invalid params"
+      "message" : "Invalid withdrawals"
     }
   },
   "statusCode" : 200

acceptance-tests/tests/src/test/resources/jsonrpc/engine/shanghai/test-cases/09_shanghai_newPayloadV2_invalid_null_withdrawals.json

@@ -28,8 +28,7 @@
     "id": 67,
     "error": {
       "code": -32602,
-      "message": "Invalid params",
-      "data": "Invalid withdrawals"
+      "message": "Invalid withdrawals"
     }
   },
   "statusCode": 200