Y24-244 - Update checkout dependency to v4

[SHIV5T3R]

Closes sanger/General-Backlog-Items#433

Changes proposed in this pull request

• Bumped checkout dependency to v4.

Instructions for Reviewers

[All PRs] - Confirm PR template filled
[Feature Branches] - Review code
[Production Merges to main]
    - Check story numbers included
    - Check for debug code
    - Check version

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.98%. Comparing base (af0cd03) to head (7af8eb2).
Report is 10 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2064   +/-   ##
========================================
  Coverage    77.98%   77.98%           
========================================
  Files          471      471           
  Lines        17975    17975           
  Branches       262      262           
========================================
  Hits         14018    14018           
  Misses        3955     3955           
  Partials         2        2           

Flag	Coverage Δ
javascript	69.89% <ø> (ø)
pull_request	77.98% <ø> (?)
push	77.98% <ø> (ø)
ruby	91.16% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[StephenHulme]

Looks good, but I think it needs a rebase