DOC: Fix groupby rendering in whatsnew (#50799)

Author: phofl

doc/source/whatsnew/v2.0.0.rst

@@ -94,10 +94,9 @@ Copy-on-Write improvements
   was added to the following methods:
 
   - :meth:`DataFrame.reset_index` / :meth:`Series.reset_index`
-  - :meth:`DataFrame.set_index` / :meth:`Series.set_index`
+  - :meth:`DataFrame.set_index`
   - :meth:`DataFrame.set_axis` / :meth:`Series.set_axis`
   - :meth:`DataFrame.rename_axis` / :meth:`Series.rename_axis`
-  - :meth:`DataFrame.rename_columns`
   - :meth:`DataFrame.reindex` / :meth:`Series.reindex`
   - :meth:`DataFrame.reindex_like` / :meth:`Series.reindex_like`
   - :meth:`DataFrame.assign`
@@ -177,8 +176,8 @@ These are bug fixes that might have notable behavior changes.
 
 .. _whatsnew_200.notable_bug_fixes.cumsum_cumprod_overflow:
 
-:meth:`.GroupBy.cumsum` and :meth:`.GroupBy.cumprod` overflow instead of lossy casting to float
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+:meth:`.DataFrameGroupBy.cumsum` and :meth:`.DataFrameGroupBy.cumprod` overflow instead of lossy casting to float
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 In previous versions we cast to float when applying ``cumsum`` and ``cumprod`` which
 lead to incorrect results even if the result could be hold by ``int64`` dtype.
@@ -824,7 +823,7 @@ Removal of prior version deprecations/changes
 
 Performance improvements
 ~~~~~~~~~~~~~~~~~~~~~~~~
-- Performance improvement in :meth:`.DataFrameGroupBy.median` and :meth:`.SeriesGroupBy.median` and :meth:`.GroupBy.cumprod` for nullable dtypes (:issue:`37493`)
+- Performance improvement in :meth:`.DataFrameGroupBy.median` and :meth:`.SeriesGroupBy.median` and :meth:`.DataFrameGroupBy.cumprod` for nullable dtypes (:issue:`37493`)
 - Performance improvement in :meth:`.DataFrameGroupBy.all`, :meth:`.DataFrameGroupBy.any`, :meth:`.SeriesGroupBy.all`, and :meth:`.SeriesGroupBy.any` for object dtype (:issue:`50623`)
 - Performance improvement in :meth:`MultiIndex.argsort` and :meth:`MultiIndex.sort_values` (:issue:`48406`)
 - Performance improvement in :meth:`MultiIndex.size` (:issue:`48723`)