Delay warning for deprecated parameter 'vert' of box and violin

The new parameter, 'orientation', was only added in the current release, so downstream wanting to avoid warnings
would require version gates. Therefore delaying by at least one release to ease the transition.

This was motivated by Pandas failing tests on this warning.

Author: ksunden

lib/matplotlib/axes/_axes.py

@@ -3875,7 +3875,7 @@ def boxplot(self, x, notch=None, sym=None, vert=None,
             control is provided by the *flierprops* parameter.
 
         vert : bool, optional
-            .. deprecated:: 3.10
+            .. deprecated:: 3.11
                 Use *orientation* instead.
 
                 If this is given during the deprecation period, it overrides
@@ -4222,7 +4222,7 @@ def bxp(self, bxpstats, positions=None, widths=None, vert=None,
             The default is ``0.5*(width of the box)``, see *widths*.
 
         vert : bool, optional
-            .. deprecated:: 3.10
+            .. deprecated:: 3.11
                 Use *orientation* instead.
 
                 If this is given during the deprecation period, it overrides
@@ -4361,9 +4361,10 @@ def merge_kw_rc(subkey, explicit, zdelta=0, usemarker=True):
             vert = mpl.rcParams['boxplot.vertical']
         else:
             _api.warn_deprecated(
-                "3.10",
+                "3.11",
                 name="vert: bool",
-                alternative="orientation: {'vertical', 'horizontal'}"
+                alternative="orientation: {'vertical', 'horizontal'}",
+                pending=True,
             )
         if vert is False:
             orientation = 'horizontal'
@@ -8642,10 +8643,11 @@ def violin(self, vpstats, positions=None, vert=None,
         # vert takes precedence.
         if vert is not None:
             _api.warn_deprecated(
-                "3.10",
+                "3.11",
                 name="vert: bool",
-                alternative="orientation: {'vertical', 'horizontal'}"
-                )
+                alternative="orientation: {'vertical', 'horizontal'}",
+                pending=True,
+            )
             orientation = 'vertical' if vert else 'horizontal'
         _api.check_in_list(['horizontal', 'vertical'], orientation=orientation)