我使用 Kubuntu 23.04
在使用“sudo apt remove steam*”然后使用“sudo apt autoremove”卸载 steam 后，我想使用经典的“sudo apt update、sudo apt upgrade 和 sudo apt autoremove”更新系统，但是当我输入“sudo apt update”时，我得到了这个：
sudo apt update
Hit:1 http://it.archive.ubuntu.com/ubuntu lunar InRelease
Hit:2 http://it.archive.ubuntu.com/ubuntu lunar-updates InRelease
Hit:3 http://it.archive.ubuntu.com/ubuntu lunar-backports InRelease
Hit:4 https://dl.google.com/linux/chrome/deb stable InRelease
Hit:5 http://security.ubuntu.com/ubuntu lunar-security InRelease
Hit:6 https://repo.steampowered.com/steam stable InRelease
Err:6 https://repo.steampowered.com/steam stable InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F24AEA9FB05498B7
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
All packages are up to date.
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://repo.steampowered.com/steam stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F24AEA9FB05498B7
W: Failed to fetch https://repo.steampowered.com/steam/dists/stable/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F24AEA9FB05498B7
W: Some index files failed to download. They have been ignored, or old ones used instead.
我该如何修复它？