DOC: Fix numpydoc section underlines (#60630)

Author: mroeschke

pandas/_libs/tslibs/nattype.pyx

@@ -704,7 +704,7 @@ class NaTType(_NaT):
         difference between the current timezone and UTC.
 
         Returns
-        --------
+        -------
         timedelta
             The difference between UTC and the local time as a `timedelta` object.
 

pandas/_libs/tslibs/timestamps.pyx

@@ -2217,7 +2217,7 @@ class Timestamp(_Timestamp):
         difference between the current timezone and UTC.
 
         Returns
-        --------
+        -------
         timedelta
             The difference between UTC and the local time as a `timedelta` object.
 

pandas/core/strings/accessor.py

@@ -3700,7 +3700,7 @@ def casefold(self):
     Series.str.isupper : Check whether all characters are uppercase.
 
     Examples
-    ------------
+    --------
     The ``s5.str.istitle`` method checks for whether all words are in title
     case (whether only the first letter of each word is capitalized). Words are
     assumed to be as any sequence of non-numeric characters separated by