Investigate `test_variables_put` in `test_dds.py`

Currently marked as xfail
This test fails with `AssertionError: Calls not found.`
Here is the output when it fails:
```
lib/python3.12/unittest/mock.py:986: AssertionError
=========================================================================== warnings summary ===========================================================================
cdds/tests/test_deprecated/test_transfer/test_dds.py::TestVarDistinctness::test_pattern_match_sufficiently_distinct_on_local
cdds/deprecated/transfer/drs.py:562: FutureWarning: Possible nested set at position 1
tidy_facet = re.sub(r"[[\]]", "", facet)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
======================================================================= short test summary info ========================================================================
FAILED cdds/cdds/tests/test_deprecated/test_transfer/test_dds.py::TestMoosePut::test_several_variables_put - AssertionError: Calls not found.
```
It started failing during the update of iris and python in this issue https://github.com/MetOffice/CDDS/pull/774

https://github.com/MetOffice/CDDS/pull/774/files/e732cce8e09a482698a0be2724d520ce58b74129#diff-ad0628902a391adb87c8c4a614f2f315225e04d2c0f0e5e3872ead7bf0c09d04

Start with cdds/tests/test_deprecated/test_transfer/test_dds.py and run TestMoosePut::test_several_variables_put to reproduce the AssertionError. Review its xfail marker and compare the relevant changes in pull request 774, then trace the expected mock calls. Done means the test has a justified expectation and passes without an inappropriate xfail.

Written by the indexing model from the issue text.