Library reference pages may list incompatible boards in the compatibility list

https://www.arduino.cc/reference/en/libraries/keyboard/

Arduino Uno/Mega/Nano are included in the compatibility list even though they are not compatible with the Keyboard library.

### Additional context

#### Additional reports

- https://github.com/arduino-libraries/ArduinoIoTCloud/pull/380#issuecomment-1737244158
- https://forum.arduino.cc/t/arduino-keyboard-not-working-on-arduino-uno-r3/1102400
- https://forum.arduino.cc/t/documentation-for-keyboard-library-needs-some-correction/1126221
- https://forum.arduino.cc/t/sketch-funktioniert-nicht-keyboard/1099364/6
- https://forum.arduino.cc/t/issue-on-keyboard-library/1065385
- https://forum.arduino.cc/t/what-is-wrong-here/1080550/7
- https://forum.arduino.cc/t/why-is-arduino-nano-usable-as-usb-keyboard-controller/1333682

#### Related

- https://github.com/arduino-libraries/Mouse/issues/46

Open the Keyboard library reference page at https://www.arduino.cc/reference/en/libraries/keyboard/ and inspect how its compatibility list is presented or sourced. Correct the list so Arduino Uno, Mega, and Nano are not shown as compatible with the Keyboard library, then verify the published reference page reflects the change.

Written by the indexing model from the issue text.