Add Arduino Nano Every to analogReference() page

To avoid confusion, as in this [Forum thread](https://forum.arduino.cc/t/nano-every-non-existant/1310085), add Arduino Nano Every to the **Arduino megaAVR Boards**, next to the UNO WiFi Rev2 on the [analogReference() Function page](https://docs.arduino.cc/language-reference/en/functions/analog-io/analogReference/#arduino-megaavr-boards-uno-wifi-rev2).

Open the analogReference() Function page and locate the Arduino megaAVR Boards section headed for the UNO WiFi Rev2. Review the linked forum thread for the naming context, then add Arduino Nano Every beside the existing board entry. Done means the page clearly lists both boards in that section.

Written by the indexing model from the issue text.