The repository 'http://repo.mysql.com/apt/ubuntu bionic InRelease' is not signed.
Seems you've let the repo keys expire maybe?
Currently unable to build db servers
https://dev.mysql.com/doc/refman/8.0/en/checking-gpg-signature.html?acf=1#add-comment
```
root@sat23rd:~# gpg --recv-keys 5072E1F5
gpg: keybox '/root/.gnupg/pubring.kbx' created
gpg: key 8C718D3B5072E1F5: 3 duplicate signatures removed
gpg: key 8C718D3B5072E1F5: 96 signatures not checked due to missing keys
gpg: /root/.gnupg/trustdb.gpg: trustdb created
gpg: key 8C718D3B5072E1F5: public key "MySQL Release Engineering <mysql-build@oss.oracle.com>" imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg: imported: 1
```
```
W: GPG error:
http://repo.mysql.com/apt/ubuntu bionic InRelease: The following signatures were invalid: EXPKEYSIG 8C718D3B5072E1F5 MySQL Release Engineering <mysql-build@oss.oracle.com>
E: The repository '
http://repo.mysql.com/apt/ubuntu bionic InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
```