Debug the build failures on ns4.

The error is "The key(s) in the keyring
/etc/apt/trusted.gpg.d/debian-archive-bullseye-automatic.gpg are ignored
as the file is not readable by user '_apt' executing apt-key" but it
looks like the files are owned by root:root and the permissiosn is 0644
so I'm not sure what's the issue here. Let's see.

youtube-dl/Dockerfile

 FROM docker.io/library/debian:testing
+RUN ls -l /etc/apt/trusted.gpg.d
 # hadolint ignore=DL3008,DL3015
 RUN apt-get update && \
     DEBIAN_FRONTEND=noninteractive apt-get install -y \