Update checkout version (#25)

* Update checkout version

* Update .github/workflows/0-start.yml

- Update to v3

Co-authored-by: Robert Sese <[email protected]>

* Update .github/workflows/1-enable-github-pages.yml

Co-authored-by: sinsukehlab <[email protected]>

* Update .github/workflows/5-merge-your-pull-request.yml

* Update .github/workflows/4-create-a-blog-post.yml

* Update .github/workflows/2-configure-your-site.yml

* Update .github/workflows/3-customize-your-homepage.yml

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Co-authored-by: Robert Sese <[email protected]>
Co-authored-by: sinsukehlab <[email protected]>