Latest iris broke pickle testing

[pp-mo]

See 92154ca

run detail:

==================================== ERRORS ====================================
_ ERROR collecting src/iris_grib/tests/integration/iris_integration/test_pickle_message.py _
ImportError while importing test module '/home/runner/work/iris-grib/iris-grib/src/iris_grib/tests/integration/iris_integration/test_pickle_message.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
.nox/tests-iris_source-source/lib/python3.12/importlib/__init__.py:90: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
src/iris_grib/tests/integration/iris_integration/test_pickle_message.py:13: in <module>
    from iris.tests.integration.test_pickle import Common as PickleCommon
E   ImportError: cannot import name 'Common' from 'iris.tests.integration.test_pickle' (/home/runner/work/iris-grib/iris-grib/.nox/tests-iris_source-source/lib/python3.12/site-packages/iris/tests/integration/test_pickle.py). Did you mean: 'common'?
_ ERROR collecting src/iris_grib/tests/integration/iris_integration/test_pickle_message.py _
ImportError while importing test module '/home/runner/work/iris-grib/iris-grib/src/iris_grib/tests/integration/iris_integration/test_pickle_message.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
.nox/tests-iris_source-source/lib/python3.12/importlib/__init__.py:90: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
src/iris_grib/tests/integration/iris_integration/test_pickle_message.py:13: in <module>
    from iris.tests.integration.test_pickle import Common as PickleCommon
E   ImportError: cannot import name 'Common' from 'iris.tests.integration.test_pickle' (/home/runner/work/iris-grib/iris-grib/.nox/tests-iris_source-source/lib/python3.12/site-packages/iris/tests/integration/test_pickle.py). Did you mean: 'common'?
=============================== warnings summary ===============================
.nox/tests-iris_source-source/lib/python3.12/site-packages/pyproj/network.py:[59](https://github.com/SciTools/iris-grib/actions/runs/13629976762/job/38095397704#step:11:60)
  /home/runner/work/iris-grib/iris-grib/.nox/tests-iris_source-source/lib/python3.12/site-packages/pyproj/network.py:59: UserWarning: pyproj unable to set PROJ database path.
    _set_context_ca_bundle_path(ca_bundle_path)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=========================== short test summary info ============================
ERROR src/iris_grib/tests/integration/iris_integration/test_pickle_message.py
ERROR src/iris_grib/tests/integration/iris_integration/test_pickle_message.py
!!!!!!!!!!!!!!!!!!! Interrupted: 2 errors during collection !!!!!!!!!!!!!!!!!!!!

[trexfeathers]

Closed by #620