Merge pull request #22311 from meeseeksmachine/auto-backport-of-pr-22…

…285-on-v3.5.x

Backport PR #22285 on branch v3.5.x (Don't warn on grid removal deprecation if grid is hidden)

lib/matplotlib/axes/_axes.py

@@ -5617,8 +5617,11 @@ def _interp_grid(X):
         return X, Y, C, shading
 
     def _pcolor_grid_deprecation_helper(self):
-        if any(axis._major_tick_kw["gridOn"]
-               for axis in self._get_axis_list()):
+        grid_active = any(axis._major_tick_kw["gridOn"]
+                          for axis in self._get_axis_list())
+        # explicit is-True check because get_axisbelow() can also be 'line'
+        grid_hidden_by_pcolor = self.get_axisbelow() is True
+        if grid_active and not grid_hidden_by_pcolor:
             _api.warn_deprecated(
                 "3.5", message="Auto-removal of grids by pcolor() and "
                 "pcolormesh() is deprecated since %(since)s and will be "