To manually add the GPG key to your system:
# Download and add to apt keyring
curl -fsSL https://debs.golder.tech/pubkey.gpg | sudo gpg --dearmor -o /usr/share/keyrings/golder-tech.gpg
# Or import directly
gpg --import https://debs.golder.tech/pubkey.gpg
253A7E508D2D59CDEFB85022889C4DB3D8EB0D26253A7E508D2D59CDrossigee-extras <support@golder.tech>