esp32: Bump version to 1.7.3.b2.
esp32: Bump version to 1.7.3.b2.

husigeza/pycom-micropython-sigfox,husigeza/pycom-micropython-sigfox,Xykon/pycom-micropython-sigfox,Xykon/pycom-micropython-sigfox,husigeza/pycom-micropython-sigfox,Xykon/pycom-micropython-sigfox,husigeza/pycom-micropython-sigfox,Xykon/pycom-micropython-sigfox,husigeza/pycom-micropython-sigfox,Xykon/pycom-micropython-sigfox