Given conf-regen hooks check if the key exists and, if yes, skip redownloading:
sudo rm /etc/apt/trusted.gpg.d/extra_php_version.gpg, then sudo yunohost tools regen-conf apt --force
Alternatively just fetch the current key (adopted from core scripts:
curl -sL "https://packages.sury.org/php/apt.gpg" | gpg --dearmor | sudo tee "/etc/apt/trusted.gpg.d/extra_php_version.gpg" > /dev/null