DOC: add whatsnew entry for bug fix (#25190)

Author: YagoGG

doc/source/whatsnew/v1.1.0.rst

@@ -158,6 +158,7 @@ Indexing
 - Bug in :meth:`PeriodIndex.is_monotonic` incorrectly returning ``True`` when containing leading ``NaT`` entries (:issue:`31437`)
 - Bug in :meth:`DatetimeIndex.get_loc` raising ``KeyError`` with converted-integer key instead of the user-passed key (:issue:`31425`)
 - Bug in :meth:`Series.xs` incorrectly returning ``Timestamp`` instead of ``datetime64`` in some object-dtype cases (:issue:`31630`)
+- Bug in :meth:`DataFrame.interpolate` raising ``UnboundLocalError`` when specifying the ``axis`` with a string (:issue:`25190`)
 
 Missing
 ^^^^^^^