Remove build warning by updating task to actions/checkout@v4

[seantleonard]

Why This Change?

Even though builds are successful, we still get a few warnings that need mitigation due to old versions of github actions used.

What is this change?

• Updates GitHub Actions actions/checkout to use v4 as latest. actions/checkout@v4
  • per: https://github.com/actions/checkout/releases/tag/v4.1.7
  • See GitHub docs for syntax on referring to "reusable" GitHub Actions tasks: https://docs.github.com/en/actions/using-workflows/reusing-workflows#calling-a-reusable-workflow

You reference reusable workflow files using one of the following syntaxes:

{owner}/{repo}/.github/workflows/{filename}@{ref} for reusable workflows in public and private repositories. ./.github/workflows/{filename} for reusable workflows in the same repository.

In the first option, {ref} can be a SHA, a release tag, or a branch name. If a release tag and a branch have the same name, the release tag takes precedence over the branch name. Using the commit SHA is the safest option for stability and security. For more information, see "Security hardening for GitHub Actions."

[seantleonard]

Waiting to confirm successful execution of checkout task in this run: https://github.com/microsoft/sqlmlutils/actions/runs/9703950338/job/26783155067?pr=117

[seantleonard]

all good.