apt updateすると、heroku cliでエラー
sudo apt update
...
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.
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