tests/arch/xilinx: Fix for warnings on boxes

The two test scripts affected use boxed modules directly; under normal usage the warning shouldn't appear.

tests/arch/xilinx/dsp_abc9.ys

@@ -1,4 +1,5 @@
 logger -nowarn "Yosys has only limited support for tri-state logic at the moment\. .*"
+logger -nowarn "Ignoring boxed module .*\."
 
 read_verilog <<EOT
 module top(input [24:0] A, input [17:0] B, output [47:0] P);