Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Several jobs in example_mirror.yml and example_github.yml use ubuntu-20.04 runners, which GitHub removed on April 15, 2025. These jobs fail on every run.

Affected jobs

• example_mirror.yml: known-version, latest-version-linux-macos, known-version-linux-macos, known-version-linux
• example_github.yml: known-version, latest-version-linux-macos, known-version-linux-macos

Suggested fix

Replace ubuntu-20.04 with ubuntu-latest (or ubuntu-24.04).