[Silabs] Add missing space at the end of --icd macro (#33049)

Author: mkardous-silabs

scripts/examples/gn_silabs_example.sh

@@ -193,7 +193,7 @@ else
                 shift
                 ;;
             --icd)
-                optArgs+="chip_enable_icd_server=true chip_openthread_ftd=false sl_enable_test_event_trigger=true"
+                optArgs+="chip_enable_icd_server=true chip_openthread_ftd=false sl_enable_test_event_trigger=true "
                 shift
                 ;;
             --low-power)