Update GitHub Actions to use newer versions

[madrob]

Update checkout action to latest version.
Update swiftlang workflows to latest versions.
Update Xcode version selection.

Replace this paragraph with a description of your changes and rationale. Provide links to an existing issue or external references/discussions, if appropriate.

Checklist

• I've added at least one test that validates that my change is working, if appropriate
• I've followed the code style of the rest of the project
• I've run Scripts/format.sh to correctly format my change
• I've read the Contribution Guidelines
• I've updated the documentation if necessary

[natecook1000]

Thanks, @madrob!