Fix: Set ValidationWorkflow as a WrapperTask

[adrien-berchet]

Description

The ValidationWorkflow is just supposed to gather sub-tasks, so by definition it should be a WrapperTask.

Checklist

This pull request is:

• A documentation / typographical error fix
  • Good to go, no issue or tests are needed
• A short code fix
  • Please include: Fixes: #<issue number> in the description if it solves an existing issue
    (which must include a complete example of the issue).
  • Please include tests that fail with the main branch and pass with the provided fix.
• A new feature implementation or update an existing feature
  • Please include: Fixes: #<issue number> in the description if it solves an existing issue
    (which must include a complete example of the feature).
  • Please include tests that cover every lines of the new/updated feature.
  • Please update the documentation to describe the new/updated feature.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (74a05cb) 100.00% compared to head (12e93e4) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #54   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            7         7           
  Lines          732       732           
  Branches       142       142           
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  Hits           732       732           

Flag	Coverage Δ
pytest	100.00% <100.00%> (ø)

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Files	Coverage Δ
data_validation_framework/task.py	100.00% <100.00%> (ø)