CI: There are no MySQL 5.7 builds for Ubuntu 20.04, this combo would have run as a container

Author: sodabrew

.github/workflows/build.yml

@@ -39,7 +39,9 @@ jobs:
           - {os: ubuntu-22.04, ruby: '3.0', db: mariadb10.6}
           - {os: ubuntu-20.04, ruby: '2.7', db: mariadb10.6}
           - {os: ubuntu-20.04, ruby: '2.7', db: mysql80}
-          - {os: ubuntu-20.04, ruby: '2.7', db: mysql57}
+
+          # MySQL 5.7 packages stopped after Ubuntu 18.04 Bionic
+          # - {os: ubuntu-18.04, ruby: '2.7', db: mysql57}
 
           # TODO - Windows CI
           # - {os: windows-2022, ruby: '3.2', db: mysql80}