👷 use latest major version for actions/checkout

[thomasmerz]

What does this PR aim to accomplish?:

Use latest major version of actions/checkout for GitHub Actions.

How does this PR accomplish the above?:

This PR changed version to latest major version for stability (do not use main/master/head in production!).

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1. I have commented my proposed changes within the code and I have tested my changes.
2. I am willing to help maintain this change if there are issues with it later.
3. I have squashed any insignificant commits. (git rebase)
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5. I have considered, and confirmed that this submission will be valuable to others.
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[yubiuser]

Thanks for your PR. However, all dependencies are up-to-date in development branch. I'll should do a release...