### Godot version

4.x (beta 5, 6, 7, 8, 9, 10) didn't tested versions before beta 5
Also reproducable in current master: c5bfe13
  
### System information

Windows 10

### Issue description

When clicking around the bottom edge of the scrollbar grabber, it is not detected as such and instead jumps to a lower position, as if you click on the free area of the scrollbar.

The red marked area is not detected as grabber click. Everything is fine on the top edge.
![image](https://user-images.githubusercontent.com/66004280/210325316-6718b793-b3ec-4c3a-b2b3-0df0f431a222.png)

### Steps to reproduce

Just use a `ScrollContainer` with e.g. a `VBox` and many `Button`s.

See the video:

https://user-images.githubusercontent.com/66004280/210325006-718e0f57-49b3-4aa1-ad35-653b9c66d9fa.mp4

### Minimal reproduction project

N/A
theme->set_stylebox("panel", "Tree", make_flat_stylebox(style_normal_color, 4, 4, 4, 5));
	theme->set_stylebox("focus", "Tree", focus);
	theme->set_stylebox("selected", "Tree", make_flat_stylebox(style_selected_color));
	theme->set_stylebox("selected_focus", "Tree", make_flat_stylebox(style_selected_color));
	theme->set_stylebox("cursor", "Tree", focus);
	theme->set_stylebox("cursor_unfocused", "Tree", focus);
	theme->set_stylebox("button_pressed", "Tree", button_pressed);
	theme->set_stylebox("title_button_normal", "Tree", make_flat_stylebox(style_pressed_color, 4, 4, 4, 4));
	theme->set_stylebox("title_button_pressed", "Tree", make_flat_stylebox(style_hover_color, 4, 4, 4, 4));
	theme->set_stylebox("title_button_hover", "Tree", make_flat_stylebox(style_normal_color, 4, 4, 4, 4));
	theme->set_stylebox("custom_button", "Tree", button_normal);
	theme->set_stylebox("custom_button_pressed", "Tree", button_pressed);
	theme->set_stylebox("custom_button_hover", "Tree", button_hover);
	theme->set_icon("checked", "Tree", icons["checked"]);
	theme->set_icon("unchecked", "Tree", icons["unchecked"]);
	theme->set_icon("indeterminate", "Tree", icons["indeterminate"]);
	theme->set_icon("updown", "Tree", icons["updown"]);
	theme->set_icon("select_arrow", "Tree", icons["option_button_arrow"]);
	theme->set_icon("arrow", "Tree", icons["arrow_down"]);
	theme->set_icon("arrow_collapsed", "Tree", icons["arrow_right"]);
	theme->set_icon("arrow_collapsed_mirrored", "Tree", icons["arrow_left"]);
	theme->set_font("title_button_font", "Tree", Ref<Font>());
	theme->set_font("font", "Tree", Ref<Font>());
	theme->set_font_size("font_size", "Tree", -1);
	theme->set_color("title_button_color", "Tree", control_font_color);
	theme->set_color("font_color", "Tree", control_font_low_color);
	theme->set_color("font_selected_color", "Tree", control_font_pressed_color);
	theme->set_color("font_outline_color", "Tree", Color(1, 1, 1));
	theme->set_color("guide_color", "Tree", Color(0.7, 0.7, 0.7, 0.25));
	theme->set_color("drop_position_color", "Tree", Color(1, 1, 1));