renovate bot needs to update the sylva-units Helm dependencies when upgrading sylva-library

The following discussion from !2892 (merged) should be addressed:

• @tmmorin started a discussion:

  @loic.nicolle @e-wyckens @mederic.deverdilhac we would need the renovate bot to be able to run the commands needed to update the sylva-units Helm dependencies: https://gitlab.com/sylva-projects/sylva-core/-/jobs/7812303665#L28

  [ERROR] sylva-units chart dependencies need to be updated with 'helm dependency update charts/sylva-units'
  The following actions are needed to make the update:
    - cd charts/sylva-units
    - helm dependency update
    - git rm charts/<old sylva-library>
    - git add charts/<new sylva-library>
    - (and then commit)