test(arch): pin the golden vectors of the last four families

Assisted-by: GLM 5.3 Flash

arch/arm64_ext.go

@@ -776,6 +776,8 @@ func (f ExtForm) Arity() int {
 	case ExtFormSveLoad, ExtFormSveStore, ExtFormNarrow, ExtFormQuadReduce, ExtFormShiftWide,
 		ExtFormConvert, ExtFormLongMul:
 		return 3
+	case ExtFormVLArith:
+		return 3
 	case ExtFormNone:
 		return 0
 	default: