update checkout action to version 4

[codecov[bot]]

Codecov Report

Merging #217 (905050a) into master (e0e02e2) will not change coverage. The diff coverage is n/a.

:exclamation: Current head 905050a differs from pull request most recent head 877df2b. Consider uploading reports for the commit 877df2b to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #217 +/- ## ======================================= Coverage 96.18% 96.18% ======================================= Files 9 9 Lines 498 498 Branches 94 94 ======================================= Hits 479 479 Misses 9 9 Partials 10 10 ```

[Gallaecio]

Thanks!