Pandas 1.5.0 results in warning on export

[bbassett-tibco]

When exporting from Python with (the recently released) Pandas 1.5.0 installed a FutureWarning is emitted:

/path/to/spotfire-python/spotfire/sbdf.py:220: FutureWarning: iteritems is deprecated and will be removed in a future version. Use .items instead.
  column_types = {str(k): _ValueTypeId.infer_from_dtype(v, f"column '{str(k)}'") for (k, v) in obj.iteritems()}

Fix the implementation of export to not emit warnings in the normal course of business.

For reference, the Pandas change at issue was pandas-dev/pandas#45321.