eth/catalyst: fail on duplicate request types (#31071)

Refer to: https://github.com/ethereum/execution-apis/pull/623

eth/catalyst/api.go

@@ -1303,7 +1303,8 @@ func validateRequests(requests [][]byte) error {
 			return fmt.Errorf("empty request: %v", req)
 		}
 		// Check that requests are ordered by their type.
-		if req[0] < last {
+		// Each type must appear only once.
+		if req[0] <= last {
 			return fmt.Errorf("invalid request order: %v", req)
 		}
 		last = req[0]