Updated github actions versions.

[MichaelClerx]

Updates checkout to v4 and setup-python to v5 to fix this warning:

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3, actions/setup-python@v4. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

And sets a python version in the style test to fix this warning:

The python-version input is not set. The version of Python currently in PATH will be used.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (81f68d8) to head (f6a8011).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1528   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           97        97           
  Lines         9665      9664    -1     
=========================================
- Hits          9665      9664    -1     

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[MichaelClerx]

@fcooper8472 @martinjrobins could you have a look please? Just an actions version update