Standard Support for Ubuntu 16.04 (Xenial Xerus) LTS has ended and it has entered Extended Security Maintenance (ESM), a paid offering from Canonical.

https://ubuntu.com/blog/ubuntu-16-04-lts-transitions-to-extended-security-maintenance-esm

So we will remove support for Ubuntu 16.04 based runners on August 1, 2021. It is highly recommended that you upgrade ubuntu-16.04 workflows to ubuntu-18.04 or ubuntu-20.04 (alias ubuntu-latest).

Notes:

• ppa:ondrej/php has deleted Ubuntu 16.04 builds, so we have switched to a mirror of the PPA till the support is removed on August 1, 2021. Till that time Ubuntu 16.04 will not receive any updates to PHP versions or extensions. So please upgrade!

• Many projects in past used ubuntu-16.04 because PHP 5.6 to 8.0 are pre-installed on it. We recently switched to cached PHP builds, which reduces the setup time to less than 5 sec for these versions, pre-installed or not. So you can upgrade the OS environment without any major changes in CI run time.

Thanks
Shivam Mathur