How to update Gitlab repository public key

[email protected]:~$ sudo apt update
[sudo] password for brennan:
Hit:1 http://security.ubuntu.com/ubuntu bionic-security InRelease
Hit:2 http://archive.ubuntu.com/ubuntu bionic InRelease
Hit:4 http://archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit:5 http://archive.ubuntu.com/ubuntu bionic-backports InRelease
Get:3 https://packages.gitlab.com/gitlab/gitlab-ee/ubuntu bionic InRelease [23.3 kB]
Err:3 https://packages.gitlab.com/gitlab/gitlab-ee/ubuntu bionic InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3F01618A51312F3F
Fetched 23.3 kB in 1s (24.3 kB/s)
Reading package lists... Done
Building dependency tree
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://packages.gitlab.com/gitlab/gitlab-ee/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3F01618A51312F3F
W: Failed to fetch https://packages.gitlab.com/gitlab/gitlab-ee/ubuntu/dists/bionic/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3F01618A51312F3F
W: Some index files failed to download. They have been ignored, or old ones used instead.

I recently went to update my self-hosted Gitlab instance on Ubuntu 18.04 and got a new error: NO_PUBKEY 3F01618A51312F3F

To fix this just re-import the public key of the repository and run the apt update again.

curl --silent https://packages.gitlab.com/gpg.key | sudo apt-key add -

Happy coding!