Silent failure when DNS fail to resolve

[corvus-ch]

Testing things for #1055, revealed that failure of DNS resolution did not result in any feedback to the user. I just looked like there were just no new videos to download.

Steps to reproduce:

podman run --rm -it ghcr.io/jmbannon/ytdl-sub:latest bash
echo "nameserver 0.0.0.0" > /etc/resolv.conf
cat <<EOF > /config/config.yml
configuration:
  working_directory: "/config"

presets:
  base:
    overrides:
      tv_show_directory: "/data/shows"

  TV Show:
    preset:
      - "Only Recent"
      - "Jellyfin TV Show by Date"
      - "base"
EOF
cat <<EOF > /config/subscription.yml
TV Show:
  = MyTag:
    "My Channel": "https://www.youtube.com/@MyChannel"
EOF
/usr/bin/ytdl-sub --config=/config/cfg.yaml sub /config/foo.yaml
[ytdl-sub] Validating subscriptions...
[ytdl-sub] Beginning subscription download for My Channel
[ytdl-sub:downloader] Beginning downloads for https://www.youtube.com/@MyChannel
[ytdl-sub] 
No files changed for My Channel
[ytdl-sub] Download Summary:
My Channel     0 0 0     5 ✔
Total: 1               0 0 0     5 Success

Obviously, you have to use the URL of an actual channel.

Expectation: Some kind of indication, that looking up the list of available videos did fail.