Delay warning for deprecated parameter 'vert' of box and violin on 3.10

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.

This portion is made direct to v3.10.x with matplotlib#29155 being the accompanying version to edit the deprecation on main.

Reinstate warning as a pending warning

STY: fits on one line

lib/matplotlib/axes/_axes.py

@@ -3875,9 +3875,11 @@ 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.
 
+                This is a pending deprecation for 3.10, with full deprecation
+                in 3.11 and removal in 3.13.
                 If this is given during the deprecation period, it overrides
                 the *orientation* parameter.
 
@@ -4222,9 +4224,11 @@ 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.
 
+                This is a pending deprecation for 3.10, with full deprecation
+                in 3.11 and removal in 3.13.
                 If this is given during the deprecation period, it overrides
                 the *orientation* parameter.
 
@@ -4361,9 +4365,10 @@ 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 +8647,11 @@ 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)
 

lib/matplotlib/tests/test_axes.py

@@ -9315,7 +9315,9 @@ def test_violinplot_orientation(fig_test, fig_ref):
     # Compare images between a figure that
     # uses vert and one that uses orientation.
     ax_ref = fig_ref.subplots()
-    ax_ref.violinplot(all_data, vert=False)
+
+    with pytest.warns(PendingDeprecationWarning, match='vert: bool'):
+        ax_ref.violinplot(all_data, vert=False)
 
     ax_test = fig_test.subplots()
     ax_test.violinplot(all_data, orientation='horizontal')