Function export_github_action 

pub fn export_github_action(
    session: &Session,
    params: Option<&[Parameter]>,
) -> String

Export a session as a GitHub Actions workflow YAML.

Generates a workflow with:

• Metadata header comments (session name, date, command count)
• Trigger on push to main
• Single build job on ubuntu-latest
• env: block when parameters are provided
• Checkout step followed by one step per command
• working-directory on every step
• Annotations for failed commands (non-zero exit codes)

When params is Some, an env: block is added at job level and commands use $VAR references.

Empty sessions produce a valid workflow with a “No commands recorded” comment.