How do I fix this apt error when trying to update?

Question

I’m not sure what I did before, but now I can’t run apt-get update. Any ideas on how to recover from this?

sudo apt-get update

Get:1 https://cli.github.com/packages focal InRelease [3741 B]
Hit:2 http://us.archive.ubuntu.com/ubuntu focal InRelease                 
Hit:3 https://download.docker.com/linux/ubuntu focal InRelease            
Hit:4 http://us.archive.ubuntu.com/ubuntu focal-updates InRelease
Hit:5 http://us.archive.ubuntu.com/ubuntu focal-backports InRelease
Hit:6 http://us.archive.ubuntu.com/ubuntu focal-security InRelease
Err:1 https://cli.github.com/packages focal InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C99B11DEB97541F0
Reading package lists... Done
W: GPG error: https://cli.github.com/packages focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C99B11DEB97541F0
E: The repository 'https://cli.github.com/packages focal 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.