Explicitly list the supported architectures (samd, mbed_portenta) as verified by CI build. (arduino-libraries#35)

Author: aentinger

library.properties

@@ -6,5 +6,5 @@ sentence=Enables sending and receiving data using the RS-485 standard with RS-48
 paragraph=This library supports the Maxim Integrated MAX3157 and equivalent chipsets.
 category=Communication
 url=http://www.arduino.cc/en/Reference/ArduinoRS485
-architectures=*
+architectures=samd,mbed_portenta
 includes=ArduinoRS485.h