NCP-update 1.46.1 to 1.47.0 error

Hi!
Tis is my first post and I hope I’m right her.
I tried to update my NextcloudPi from v1.46.10 to v1.47.0 via SSH. The update aborted with an error. The following message was displayed:

pi@nextcloudpi:~ $ sudo ncp-update
Downloading updates
Performing updates
● prometheus-node-exporter.service - Prometheus exporter for machine metrics
Loaded: loaded (/lib/systemd/system/prometheus-node-exporter:service; disabled; vendor preset: enabled)
Active: inactive (dead)
Docs: GitHub - prometheus/node_exporter: Exporter for machine metrics
Unit ncp-metrics-exporter.service could not be found.
Installing metrics
Hit:1 htxxx deb.debian:org/debian buster InRelease
Hit:2 htxxx deb.debian:org/debian-security buster/updates InRelease
Hit:3 htxxx deb.debian:org/debian buster-updates InRelease
Hit:4 htxxx archive.raspberrypi:org/debian buster InRelease
Get:5 htxxx packages.cisofy:com/community/lynis/deb stable InRelease [11.4 kB]
Err:5 https://packages.cisofy.com/community/lynis/deb stable InRelease
The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 9DE922F1C2FDE6C4
Reading package lists… Done
W: GPG error: https://packages.cisofy.com/community/lynis/deb stable InRelease: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 9DE922F1C2FDE6C4
E: The repository ‘https://packages.cisofy.com/community/lynis/deb stable InRelease’ is not signed.
N: Updating from such a repository can’t be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
Error while applying update 1.47.0. Exiting…
pi@nextcloudpi:~ $

The same happens when trying to start ncp-update via the web-gui.
Is there a solution to update the ncp anyway?
Thank you for your help!
Stephan P.