### 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("selected", "ItemList", make_flat_stylebox(style_selected_color));
	theme->set_stylebox("selected_focus", "ItemList", make_flat_stylebox(style_selected_color));
	theme->set_stylebox("cursor", "ItemList", focus);
	theme->set_stylebox("cursor_unfocused", "ItemList", focus);
	theme->set_constant("outline_size", "ItemList", 0);
	
	Ref<StyleBoxFlat> style_tab_selected = make_flat_stylebox(style_normal_color, 10, 4, 10, 4, 0);
	style_tab_selected->set_border_width(SIDE_TOP, Math::round(2 * scale));
	style_tab_selected->set_border_color(style_focus_color);
	Ref<StyleBoxFlat> style_tab_unselected = make_flat_stylebox(style_pressed_color, 10, 4, 10, 4, 0);
	
	style_tab_unselected->set_border_width(SIDE_LEFT, Math::round(scale));
	style_tab_unselected->set_border_width(SIDE_RIGHT, Math::round(scale));
	style_tab_unselected->set_border_color(style_popup_border_color);
	Ref<StyleBoxFlat> style_tab_disabled = style_tab_unselected->duplicate();
	style_tab_disabled->set_bg_color(style_disabled_color);
	theme->set_stylebox("tab_selected", "TabContainer", style_tab_selected);
	theme->set_stylebox("tab_unselected", "TabContainer", style_tab_unselected);
	theme->set_stylebox("tab_disabled", "TabContainer", style_tab_disabled);
	theme->set_stylebox("panel", "TabContainer", make_flat_stylebox(style_normal_color, 0, 0, 0, 0));
	theme->set_stylebox("tabbar_background", "TabContainer", make_empty_stylebox(0, 0, 0, 0));
	theme->set_icon("increment", "TabContainer", icons["scroll_button_right"]);
	theme->set_icon("increment_highlight", "TabContainer", icons["scroll_button_right_hl"]);
	theme->set_icon("decrement", "TabContainer", icons["scroll_button_left"]);
	theme->set_icon("decrement_highlight", "TabContainer", icons["scroll_button_left_hl"]);
	theme->set_icon("drop_mark", "TabContainer", icons["tabs_drop_mark"]);
	theme->set_icon("menu", "TabContainer", icons["tabs_menu"]);
	theme->set_icon("menu_highlight", "TabContainer", icons["tabs_menu_hl"]);
	theme->set_font("font", "TabContainer", Ref<Font>());
	theme->set_font_size("font_size", "TabContainer", -1);