Replace v2 of checkout with v4 as warning received in pipeline:

'The following actions uses node12 which is deprecated and will
 be forced to run on node16: actions/checkout@v2,
 actions/setup-python@v2.
 For more info:
 https://github.blog/changelog/
 2023-06-13-github-actions-all-actions-will-run-on-node16-instead
 -of-node12-by-default/'

AB#8731