Upgrade to checkout v4

[eivindjahren]

Pre review checklist

• Read through the code changes carefully after finishing work
• Make sure tests pass locally (after every commit!)
• Wait for tests in CI to pass (see "checks" below)
• Prepare changes in small commits for more convenient review (optional)
• PR title captures the intent of the changes, and is fitting for release notes.
• Updated documentation
• Ensured new behaviour is tested (opened GUI? screenshots? tried workflows?)
• Commit history is consistent and clean, in line with the contribution guidelines.

Pre merge checklist

• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution
  guidelines.

[codecov-commenter]

Codecov Report

Merging #6041 (3e287ad) into main (a46cb83) will decrease coverage by 0.03%.
Report is 2 commits behind head on main.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #6041      +/-   ##
==========================================
- Coverage   82.56%   82.54%   -0.03%     
==========================================
  Files         352      352              
  Lines       21897    21897              
  Branches      826      826              
==========================================
- Hits        18080    18074       -6     
- Misses       3518     3524       +6     
  Partials      299      299              

see 4 files with indirect coverage changes

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[andreas-el]

Lets go! 🚀