How to GPG sign builds?

[vadi2]

GPG signing is failing for me with:

FB: Running: flatpak build-export --arch=x86_64 --gpg-sign=*** '--exclude=/lib/debug/*' --include=/lib/debug/app '--exclude=/share/runtime/locale/*/*' /__w/Mudlet/Mudlet/repo flatpak_app master
error: Failure signing commit file: Pinentry: Inappropriate ioctl for device

According to https://stackoverflow.com/a/57591830/72944, setting the GPG_TTY environment variable should do it. Is there a way to have the action set it, or any other way to get GPG signing to work?