Pandas FutureWarning: Length 1 tuple will be returned

[R-Palazzo]

Problem Description

Running the sdv/tests with pytests raised the following pandas warning:

FutureWarning: In a future version of pandas, a length 1 tuple will be returned when iterating over a groupby with a grouper equal to a list of length 1. Don't supply a list with a single grouper to avoid this warning.

Expected behavior

We want to modify the code to no longer get this warning.

Additional context

Here is given the code lines in sdv that raised the warning. Because this list may be incomplete, it would be nice to check after the correction that the warning is not in the warning summary of pytests.

Lines to be modified:

/sdv/constraints/base.py:502
/sdv/single_table/base.py:889
/sdv/sequential/par.py:138
/sdv/single_table/base.py:927