Review and update GaussianCopula Unit Tests

[csala]

The GaussianCopula class underwent a few changes that were not fully taken into account on the unit tests side.

As a consequence, even though the tests do not fail, some tests set up a few unnecessary things and do not do all the necessary checks.

An example of this is the test__update_metadata, which mocks a self.get_model_kwargs return value that is later on not really used in the code being tested.

SDV/tests/unit/tabular/test_copulas.py

Line 149 in f4bfb07

def test__update_metadata(self):

To fix this, the unit tests from the tests/unit/tabular/test_copulas.py module should be reviewed and updated appropriately.