A matrix strategy allows you to define different versions of a programming language (or any other environment setting) and run tests on each version simultaneously. This is particularly useful for testing code compatibility across different versions of a language.
A matrix strategy can also be used to test code on multiple operating systems (e.g., Windows, macOS, Linux) by defining these operating systems as matrix variables. This enables cross-platform testing within the same workflow.

A non-zero exit code is used to set the status of an action to "failed" in GitHub Actions. When the action's script or code exits with a non-zero status, it indicates failure, and GitHub will mark the action as failed.

Any actions or reusable workflows stored in the internal or private repository can be used in workflows defined in other internal or private repositories owned by the same organization, or by any organization owned by the enterprise.
Reference:
https://docs.github.com/actions/creating-actions/sharing-actions-and-workflows-with-your- enterprise

[B] If you want your GitHub Enterprise Server instance to use third-party custom actions, you need to enable GitHub Connect.
[C] Most official GitHub-authored actions are automatically bundled with GitHub Enterprise Server, and are captured at a point in time from GitHub Marketplace.
[F] Third-party actions can be manually synchronized to GitHub Enterprise Server (GHES) to be used in workflows without requiring an internet connection to GitHub.com. This is done using the actions-sync tool to download actions from GitHub.com and transfer them to the GHES instance.
This manual method provides an alternative to using GitHub Connect, offering stricter control over which actions are available on the GHES instance.
Reference:
https://docs.github.com/en/[email protected]/get-started/exploring-integrations/about- using-integrations
https://docs.github.com/en/[email protected]/admin/managing-github-actions-for-your- enterprise/managing-access-to-actions-from-githubcom/about-using-actions-in-your-enterprise

Example: Setting a debug message
echo "::debug::Set the Octocat variable"
Reference:
https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-commands