BUG: Allow pd.unique to accept tuple of strings
 - [x] tests added / passed
 - [x] passes ``git diff upstream/master -u -- "*.py" | flake8 --diff``
 - [x] whatsnew entry

xref #17077

 `pd.unique()` calls `_ensure_arraylike` which did not accept tuples that contains strings. Converts tuple to list first before dispatching to `list_to_object_array`