chore(deps): update actions/checkout action to v6

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
actions/checkout	action	major	v4 → v6

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Release Notes

actions/checkout (actions/checkout)

v6

Compare Source

v5

Compare Source

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Configuration

📅 Schedule: Branch creation - "after 7am and before 4pm on monday" in timezone Europe/London, Automerge - At any time (no schedule defined).

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♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.90%. Comparing base (4a4f816) to head (faebb5a).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #290   +/-   ##
=======================================
  Coverage   76.90%   76.90%           
=======================================
  Files          31       31           
  Lines        4533     4533           
  Branches      322      322           
=======================================
  Hits         3486     3486           
  Misses        978      978           
  Partials       69       69           

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