Because `ShellCheck` comes pre-installed on the GitHub Actions virtual environment we're using for this workflow (`ubuntu-latest`), we don't need to include the installation commands for ShellCheck.
Read more on the GitHub Actions Virtual Environments [[ https://github.com/actions/virtual-environments/blob/main/images/linux/Ubuntu2004-Readme.md | README ]] for `ubuntu-latest`, under the “Installed apt packages” section.