Update my PGP key, in case anyone looks here for it.

Cue the song "Signs of Life" from Pink Floyd. I haven't dropped off
the earth just yet, although it's been awhile since I updated my PGP
key in the official documentation.

NB: This key includes my email address at Proton, but right now this
PGP key won't work if you use it when sending mail to that account. I
still need to figure out how to fix that.