Standard Support for Ubuntu 20.04 (Focal Fossa) LTS will end soon, as it enters Extended Security Maintenance (ESM), a paid offering from Canonical.
Ref: https://ubuntu.com/blog/ubuntu-20-04-lts-end-of-life-standard-support-is-coming-to-an-end-heres-how-to-prepare

GitHub Actions has planned to remove support for the environment ubuntu-20.04 on April 15, 2025.
Ref: actions/runner-images#11101

Consequently, this action will remove support for Ubuntu 20.04 environments on April 15, 2023, on GitHub-hosted ubuntu-20.04 runner and self-hosted environments. So please upgrade ubuntu-20.04 workflows to ubuntu-22.04 or ubuntu-24.04 (alias ubuntu-latest) both on GitHub-hosted environments and self-hosted environments on your base OS as well as in the containers.