When i tries to update and upgrade my apt i get these errors below:
Get:1 https://cli.github.com/packages stable InRelease [3 743 B]
Hit:2 http://ppa.launchpad.net/git-core/ppa/ubuntu focal InRelease
Err:1 https://cli.github.com/packages stable InRelease
The following signatures were invalid: EXPKEYSIG C99B11DEB97541F0 Nate Smith <vilmibm@github.com>
Hit:3 http://ppa.launchpad.net/zorinos/apps/ubuntu focal InRelease
Hit:4 http://ppa.launchpad.net/zorinos/drivers/ubuntu focal InRelease
Hit:5 http://security.ubuntu.com/ubuntu focal-security InRelease
Hit:6 http://ppa.launchpad.net/zorinos/patches/ubuntu focal InRelease
Hit:7 http://ppa.launchpad.net/zorinos/stable/ubuntu focal InRelease
Hit:8 https://packages.zorinos.com/stable focal InRelease
Hit:9 https://packages.zorinos.com/patches focal InRelease
Hit:10 https://packages.zorinos.com/apps focal InRelease
Hit:11 https://packages.zorinos.com/drivers focal InRelease
Hit:12 http://se.archive.ubuntu.com/ubuntu focal InRelease
Hit:13 http://se.archive.ubuntu.com/ubuntu focal-updates InRelease
Hit:14 http://se.archive.ubuntu.com/ubuntu focal-backports InRelease
Reading package lists... Done
W: GPG error: https://cli.github.com/packages stable InRelease: The following signatures were invalid: EXPKEYSIG C99B11DEB97541F0 Nate Smith <vilmibm@github.com>
E: The repository 'https://cli.github.com/packages 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.
And i have tried with this commands below to flush my cache?
sudo rm /var/lib/apt/lists/* -vf
sudo apt-get clean
sudo apt-get update
sudo apt-get upgrade
But it hasn't worked how can i solve this problem?