unable to update linux lite 4.8

[Blinmakerivan]

Hi,
i am using linux lite 4.8 and i am unable to update . when ever I run "Install Updates" it returns the following errors

Get:1 http://repo.mysql.com/apt/ubuntu bionic InRelease [19.4 kB]
Hit:2 http://ppa.launchpad.net/bartbes/love-stable/ubuntu bionic InRelease
Hit:3 http://uk-mirrors.evowise.com/ubuntu bionic InRelease
Hit:4 http://dl.google.com/linux/chrome/deb stable InRelease
Hit:5 http://repo.linuxliteos.com/linuxlite diamond InRelease
Err:1 http://repo.mysql.com/apt/ubuntu bionic InRelease
  The following signatures were invalid: EXPKEYSIG 8C718D3B5072E1F5 MySQL Release Engineering <[email protected]>
Hit:6 http://archive.canonical.com/ubuntu bionic InRelease
Hit:7 http://ppa.launchpad.net/deadsnakes/ppa/ubuntu bionic InRelease
Get:8 http://uk-mirrors.evowise.com/ubuntu bionic-security InRelease [88.7 kB]
Hit:9 http://ppa.launchpad.net/teejee2008/ppa/ubuntu bionic InRelease
Get:10 http://uk-mirrors.evowise.com/ubuntu bionic-updates InRelease [88.7 kB]
Hit:11 http://uk-mirrors.evowise.com/ubuntu bionic-backports InRelease
Hit:12 https://packages.microsoft.com/repos/vscode stable InRelease
Get:13 http://uk-mirrors.evowise.com/ubuntu bionic-security/main amd64 DEP-11 Metadata [46.0 kB]
Get:14 http://uk-mirrors.evowise.com/ubuntu bionic-security/universe amd64 DEP-11 Metadata [49.2 kB]
Get:15 http://uk-mirrors.evowise.com/ubuntu bionic-security/multiverse amd64 DEP-11 Metadata [2,464 B]
Get:16 http://uk-mirrors.evowise.com/ubuntu bionic-updates/main i386 Packages [714 kB]
Get:17 http://uk-mirrors.evowise.com/ubuntu bionic-updates/main amd64 Packages [1,010 kB]
Get:18 http://uk-mirrors.evowise.com/ubuntu bionic-updates/main amd64 DEP-11 Metadata [294 kB]
Get:19 http://uk-mirrors.evowise.com/ubuntu bionic-updates/universe i386 Packages [1,025 kB]
Get:20 http://uk-mirrors.evowise.com/ubuntu bionic-updates/universe amd64 Packages [1,092 kB]
Get:21 http://uk-mirrors.evowise.com/ubuntu bionic-updates/universe amd64 DEP-11 Metadata [279 kB]
Get:22 http://uk-mirrors.evowise.com/ubuntu bionic-updates/multiverse i386 Packages [7,156 B]
Get:23 http://uk-mirrors.evowise.com/ubuntu bionic-updates/multiverse amd64 Packages [11.5 kB]
Get:24 http://uk-mirrors.evowise.com/ubuntu bionic-updates/multiverse amd64 DEP-11 Metadata [2,468 B]
Reading package lists...
W: GPG error: http://repo.mysql.com/apt/ubuntu bionic InRelease: The following signatures were invalid: EXPKEYSIG 8C718D3B5072E1F5 MySQL Release Engineering <[email protected]>
E: The repository 'http://repo.mysql.com/apt/ubuntu bionic InRelease' is not signed.

Any help will be appreciated