Use Docker variables to keep versions consistent

[StephenHulme]

The Docker Node version is currently wrong

Changes proposed in this pull request

• Change node version in docker to 22
• Make it easier to update the version in the future

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 80.78%. Comparing base (df9b621) to head (5b08666).
Report is 3 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2180   +/-   ##
========================================
  Coverage    80.78%   80.78%           
========================================
  Files          476      476           
  Lines        18185    18185           
  Branches       269      269           
========================================
  Hits         14691    14691           
  Misses        3492     3492           
  Partials         2        2           

Flag	Coverage Δ
javascript	74.23% <ø> (ø)
pull_request	80.78% <ø> (-0.01%)	⬇️
push	80.78% <ø> (ø)
ruby	91.27% <ø> (ø)

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