fix:model_size collected in test 0 of model_mod_check , needed for interpolation tests

[hkershaw-brown]

Description:

model_mod_check interpolate tests need a state so runs test2 to read a state
test2 initializes an ensemble handle so needs the model_size
This pull request adds get_model_size to test 0 (test setup) so that model_size is available for use in the tests.

Fixes issue

fixes #1016

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Documentation changes needed?

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.

Tests

Please describe any tests you ran to verify your changes.
I ran the model_mod_check test 4

&model_mod_check_nml
   run_tests = 4

Checklist for merging

• Updated changelog entry
• Documentation updated
• Update conf.py

Checklist for release

• Merge into main
• Create release from the main branch with appropriate tag
• Delete feature-branch

Testing Datasets

• Dataset needed for testing available upon request
• Dataset download instructions included
• No dataset needed

[mjs2369]

Ran model_mod_check with mpi to test, good catch and solid quick fix!