Ran sudo apt update and got the following error for the Heroku repository that indicates failed signature verification and missing public key 6DB5542C356545CF. The only information about this key I can find online is in Japanese or Korean, neither of which I understand, and translating them does not reveal any particularly useful information. I am concerned this could be a MITM attack, does anyone have any information or advice?
The full 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://cli-assets.heroku.com/apt ./ InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 6DB5542C356545CF
W: Failed to fetch https://cli-assets.heroku.com/apt/./InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 6DB5542C356545CF
W: Some index files failed to download. They have been ignored, or old ones used instead.