Adapt to changes in iris structure

[stephenworsley]

Adapt to the movement of iris.experimental.ugrid to iris.mesh.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 60.86957% with 9 lines in your changes missing coverage. Please review.

Project coverage is 98.37%. Comparing base (5354829) to head (296f7fb).

Files	Patch %	Lines
esmf_regrid/__init__.py	45.45%	6 Missing :warning:
..._scheme/test_regrid_unstructured_to_rectilinear.py	57.14%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #387 +/- ## ========================================== - Coverage 98.58% 98.37% -0.21% ========================================== Files 37 37 Lines 4230 4246 +16 ========================================== + Hits 4170 4177 +7 - Misses 60 69 +9 ```

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[bjlittle]

@stephenworsley I'm just going to go ahead an merge this even though there are benchmark failures.

I guess we can sort that out post-merge 👍

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.86957% with 9 lines in your changes missing coverage. Please review.

Project coverage is 98.37%. Comparing base (5354829) to head (296f7fb). Report is 18 commits behind head on main.

Files with missing lines	Patch %	Lines
esmf_regrid/__init__.py	45.45%	6 Missing :warning:
..._scheme/test_regrid_unstructured_to_rectilinear.py	57.14%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #387 +/- ## ========================================== - Coverage 98.58% 98.37% -0.21% ========================================== Files 37 37 Lines 4230 4246 +16 ========================================== + Hits 4170 4177 +7 - Misses 60 69 +9 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.