Fix _FigureManagerGTK.resize on GTK4

Using the same method as __init__ to avoid the deprecated-in-GTK3 and
removed-in-GTK4 API.

Closes matplotlib#24015

Author: QuLogic

lib/matplotlib/backends/_backend_gtk.py

@@ -233,8 +233,8 @@ def resize(self, width, height):
         width = int(width / self.canvas.device_pixel_ratio)
         height = int(height / self.canvas.device_pixel_ratio)
         if self.toolbar:
-            toolbar_size = self.toolbar.size_request()
-            height += toolbar_size.height
+            min_size, nat_size = self.toolbar.get_preferred_size()
+            height += nat_size.height
         canvas_size = self.canvas.get_allocation()
         if self._gtk_ver >= 4 or canvas_size.width == canvas_size.height == 1:
             # A canvas size of (1, 1) cannot exist in most cases, because