Itsy M0, Hallowing: add A12 pin for PrettyPins generator

[PaintYourDragon]

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
3 out of 10 committers have signed the CLA.

:white_check_mark: hathach
:white_check_mark: RudolphRiedel
:white_check_mark: henrygab
:x: mdonoughe
:x: ladyada
:x: jepler
:x: matt-chan
:x: PaintYourDragon
:x: myelin
:x: valeros
_{You have signed the CLA already but the status is still pending? Let us recheck it.}