Fixing broken tests

[davidorme]

Description

Hopefully this fixes #390.

I think the issue is that the hydrology model needs to initialise after plants, because that populates the leaf_area_index data. That isn't explicitly set in the configuration, so then I think we are getting platform specific variation in the way TopologicalSorter is returning 'tied' models, such that plants and hydrology can vary in their execution order.

More generally - this kinda thing needs to break in a much more informative way, but the variables stuff is targeted at this (#370, #388).

Type of change

• [ ] New feature (non-breaking change which adds functionality)
• [ ] Optimization (back-end change that speeds up the code)
• [x] Bug fix (non-breaking change which fixes an issue)

Key checklist

• [x] Make sure you've run the pre-commit checks: $ pre-commit run -a
• [x] All tests pass: $ poetry run pytest

Further checks

• [ ] Code is commented, particularly in hard-to-understand areas
• [ ] Tests added that prove fix is effective or that feature works

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.18%. Comparing base (76f1906) to head (7264214).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #393 +/- ## ======================================== Coverage 93.18% 93.18% ======================================== Files 60 60 Lines 2920 2920 ======================================== Hits 2721 2721 Misses 199 199 ```

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[davidorme]

Fingers crossed!