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.

lib/matplotlib/axes/_axes.py

@@ -4360,11 +4360,15 @@ def merge_kw_rc(subkey, explicit, zdelta=0, usemarker=True):
         if vert is None:
             vert = mpl.rcParams['boxplot.vertical']
         else:
-            _api.warn_deprecated(
-                "3.10",
-                name="vert: bool",
-                alternative="orientation: {'vertical', 'horizontal'}"
-            )
+            pass
+            # Deprecation warning delayed as the alternative was only introduced in 3.10
+            #
+            # _api.warn_deprecated(
+            #     "3.11",
+            #     name="vert: bool",
+            #     alternative="orientation: {'vertical', 'horizontal'}",
+            #     pending=True,
+            # )
         if vert is False:
             orientation = 'horizontal'
         _api.check_in_list(['horizontal', 'vertical'], orientation=orientation)
@@ -8641,11 +8645,14 @@ def violin(self, vpstats, positions=None, vert=None,
         # deprecation period expires. If both are selected,
         # vert takes precedence.
         if vert is not None:
-            _api.warn_deprecated(
-                "3.10",
-                name="vert: bool",
-                alternative="orientation: {'vertical', 'horizontal'}"
-                )
+            # Deprecation warning delayed as the new api was introduced in 3.10
+            #
+            # _api.warn_deprecated(
+            #     "3.11",
+            #     name="vert: bool",
+            #     alternative="orientation: {'vertical', 'horizontal'}",
+            #     pending=True,
+            # )
             orientation = 'vertical' if vert else 'horizontal'
         _api.check_in_list(['horizontal', 'vertical'], orientation=orientation)