I resolved running:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 1397BC53640DB551
The command above download the missing key using the hexadecimal numbers given in the error (1397BC53640DB551) with apt-key. After running apt-key to download the missing PUBKEY, any packages from that repositories will be considered trusted.
It seems to be a known problem in chromium that is being worked on (check here). They are working to remove SHA1 encryption (link).
Another possible workarounds that have been posted on reddit
wget -q -O - https://dl.google.com/linux/linux_signing_key.pub | sudo apt-key add -
Looking at this, seems that Google now has two keys, and the old one will probably be discontinued along with SHA1.