title: apt-update in Azure Nvidia gives publickey error
body: <p>I started a NVIDIA VM on AZURE and trying to do update using
  <code>sudo apt update</code>
  but gives error:</p>
  <pre><code>Hit:2 http://azure.archive.ubuntu.com/ubuntu focal InRelease                                                 
  Hit:3 http://azure.archive.ubuntu.com/ubuntu focal-updates InRelease                                         
  Hit:4 http://azure.archive.ubuntu.com/ubuntu focal-backports InRelease                                   
  Hit:5 https://packages.microsoft.com/repos/azure-cli focal InRelease        
  Hit:6 http://security.ubuntu.com/ubuntu focal-security InRelease            
  Err:1 http://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64  InRelease
    The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A4B469963BF863CC
  Reading package lists... Done
  W: GPG error: http://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64  InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A4B469963BF863CC
  E: The repository 'http://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64  InRelease' is no longer 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.
  </code></pre>
  <p>to install the keys i used
  <code>sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv A4B469963BF863CC</code></p>
  <p>but that gives No data error. <code>gpg: keyserver receive failed: No data </code></p>
  <p>I can run <code>sudo apt-get upgrade</code> but not the update.
  Any help would be appreciated</p>
  <p>Even though there is cuda installed but it still doesnt find cuda libraries, and that could be due to update.</p>