Well I attempted the above in a test machine, and it sure seems like something is broke in the mysql repository.
Specifically the key seems to be expired.
# apt-key list
/etc/apt/trusted.gpg
--------------------
pub dsa1024 2003-02-03 [SCA] [expired: 2019-02-17]
A4A9 4068 76FC BD3C 4567 70C8 8C71 8D3B 5072 E1F5
uid [ expired] MySQL Release Engineering <mysql-build@oss.oracle.com>
If you really want to ignore the errors and install you could adjust your mysql.list like below. Keeping in mind this does potentially open you to someone mitm the package download.
### THIS FILE IS AUTOMATICALLY CONFIGURED ###
# You may comment out entries below, but any other modifications may be lost.
# Use command 'dpkg-reconfigure mysql-apt-config' as root for modifications.
deb [trusted=yes] http://repo.mysql.com/apt/ubuntu/ bionic mysql-apt-config
deb [trusted=yes] http://repo.mysql.com/apt/ubuntu/ bionic mysql-8.0
deb [trusted=yes] http://repo.mysql.com/apt/ubuntu/ bionic mysql-tools
#deb http://repo.mysql.com/apt/ubuntu/ bionic mysql-tools-preview
deb-src [trusted=yes] http://repo.mysql.com/apt/ubuntu/ bionic mysql-8.0
Anyway if you go this route, then you also need to know the packages seem to be named like mysql-community-* for the 8.0 packages from this repo.
# apt-cache policy mysql-community-server
mysql-community-server:
Installed: (none)
Candidate: 8.0.15-1ubuntu18.04
Version table:
8.0.15-1ubuntu18.04 500
500 http://repo.mysql.com/apt/ubuntu bionic/mysql-8.0 amd64 Packages
# apt-cache policy mysql-community-server
mysql-community-server:
Installed: (none)
Candidate: 8.0.15-1ubuntu18.04
Version table:
8.0.15-1ubuntu18.04 500
500 http://repo.mysql.com/apt/ubuntu bionic/mysql-8.0 amd64 Packages
root@01d5a926dd00:/etc/apt/sources.list.d# apt-cache show mysql-community-server
Package: mysql-community-server
Source: mysql-community
Version: 8.0.15-1ubuntu18.04
Architecture: amd64
Maintainer: MySQL Release Engineering <mysql-build@oss.oracle.com>
...
Provides: virtual-mysql-server
Homepage: http://www.mysql.com/
Priority: optional
Section: database
Filename: pool/mysql-8.0/m/mysql-community/mysql-community-server_8.0.15-1ubuntu18.04_amd64.deb
Description: MySQL Server
The MySQL(TM) software delivers a very fast, multi-threaded, multi-user,
and robust SQL (Structured Query Language) database server. MySQL Server
is intended for mission-critical, heavy-load production systems as well
as for embedding into mass-deployed software. MySQL is a trademark of
Oracle. This package includes the MySQL server binary as well as related
utilities to run and administer a MySQL server.