fix scrollbar refresh issue

Author: willmcgugan

src/textual/widget.py

@@ -3873,13 +3873,11 @@ def _scroll_update(self, virtual_size: Size) -> None:
             self.vertical_scrollbar.window_size = (
                 height - self.scrollbar_size_horizontal
             )
-            if self.vertical_scrollbar._repaint_required:
-                self.vertical_scrollbar.refresh()
+            self.vertical_scrollbar.refresh()
         if self.show_horizontal_scrollbar:
             self.horizontal_scrollbar.window_virtual_size = virtual_size.width
             self.horizontal_scrollbar.window_size = width - self.scrollbar_size_vertical
-            if self.horizontal_scrollbar._repaint_required:
-                self.horizontal_scrollbar.refresh()
+            self.horizontal_scrollbar.refresh()
 
         self.scroll_x = self.validate_scroll_x(self.scroll_x)
         self.scroll_y = self.validate_scroll_y(self.scroll_y)