Use set_window_title rather than set_label to set title of webagg figure

Author: ianthomas23

doc/api/next_api_changes/behavior/29256_IMT.rst

@@ -0,0 +1,6 @@
+Setting titles of figures using webagg backend
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Previously when using the ``webagg`` backend the title of a figure was set using
+``figure.set_label``. Now it is set using ``figure.canvas.manager.set_window_title``
+which is more consistent with other backends.

lib/matplotlib/backends/backend_webagg_core.py

@@ -328,10 +328,8 @@ def handle_toolbar_button(self, event):
         getattr(self.toolbar, event['name'])()
 
     def handle_refresh(self, event):
-        figure_label = self.figure.get_label()
-        if not figure_label:
-            figure_label = f"Figure {self.manager.num}"
-        self.send_event('figure_label', label=figure_label)
+        if self.manager:
+            self.send_event('figure_label', label=self.manager.get_window_title())
         self._force_full = True
         if self.toolbar:
             # Normal toolbar init would refresh this, but it happens before the