Expired APT repository key

[ciaby]

Summary

The APT repository for Mattermost is currently broken (expired APT repository key)

Steps to reproduce

Install the APT repository using this command:
curl -o- https://deb.packages.mattermost.com/setup-repo.sh | sudo bash
Try to install mattermost or mattermost-desktop:
sudo apt install mattermost

Expected behavior

Mattermost should be installed as a Debian/Ubuntu package.

Observed behavior (that appears unintentional)

I get this error message:
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://deb.packages.mattermost.com focal InRelease: The following signatures were invalid: EXPKEYSIG F8F2C31744774B28 Mattermost Build <dev-ops@mattermost.com> W: Failed to fetch https://deb.packages.mattermost.com/dists/focal/InRelease The following signatures were invalid: EXPKEYSIG F8F2C31744774B28 Mattermost Build <dev-ops@mattermost.com> W: Some index files failed to download. They have been ignored, or old ones used instead.

Possible fixes

The signing key for the APT repository is expired and should be renewed.

[amyblais]

Closing as a duplicate of #26707 (comment).