docs(whatsnew): add change for degenerate distribution

Author: Alvaro-Kothe

doc/source/whatsnew/v3.0.0.rst

@@ -1166,6 +1166,7 @@ Groupby/resample/rolling
 - Bug in :meth:`Rolling.apply` for ``method="table"`` where column order was not being respected due to the columns getting sorted by default. (:issue:`59666`)
 - Bug in :meth:`Rolling.apply` where the applied function could be called on fewer than ``min_period`` periods if ``method="table"``. (:issue:`58868`)
 - Bug in :meth:`Rolling.skew` incorrectly computing skewness for windows following outliers due to numerical instability. The calculation now properly handles catastrophic cancellation by recomputing affected windows (:issue:`47461`)
+- Bug in :meth:`Rolling.skew` incorrectly returning ``0.0`` for constant-value windows. Now returns ``NaN`` to match the statistical definition of skewness for degenerate distributions
 - Bug in :meth:`Series.resample` could raise when the date range ended shortly before a non-existent time. (:issue:`58380`)
 
 Reshaping