Modernize GitHub Actions workflows #44
                
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Summary
This PR updates the GitHub Actions workflows to use modern, supported versions and fixes a syntax error.
Changes
actions/checkoutfrom v1 to v4 in multiple workflows (actions.yml, env.yml, container.yml)Motivation
actions/checkout@v1is very outdated and should be updated to v4 for security and compatibilityTesting
The updated workflows should run successfully on this PR to verify the changes work correctly.