### 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
#include "default_theme.h"
#include "core/os/os.h"
#include "default_font.gen.h"
#include "default_theme_icons.gen.h"
#include "scene/resources/font.h"
#include "scene/resources/theme.h"
#include "scene/theme/theme_db.h"
#include "servers/text_server.h"
#include "modules/modules_enabled.gen.h" 
#ifdef MODULE_SVG_ENABLED
#include "modules/svg/image_loader_svg.h"
#endif
static const int default_font_size = 16;
static float scale = 1.0;
static const int default_margin = 4;
static const int default_corner_radius = 3;
static Ref<StyleBoxFlat> make_flat_stylebox(Color p_color, float p_margin_left = default_margin, float p_margin_top = default_margin, float p_margin_right = default_margin, float p_margin_bottom = default_margin, int p_corner_radius = default_corner_radius, bool p_draw_center = true, int p_border_width = 0) {
	Ref<StyleBoxFlat> style(memnew(StyleBoxFlat));
	style->set_bg_color(p_color);
	style->set_default_margin_individual(p_margin_left * scale, p_margin_top * scale, p_margin_right * scale, p_margin_bottom * scale);
	style->set_corner_radius_all(p_corner_radius);
	style->set_anti_aliased(true);
	
	style->set_corner_detail(MIN(Math::ceil(1.5 * p_corner_radius), 6) * scale);
	style->set_draw_center(p_draw_center);
	style->set_border_width_all(p_border_width);
	return style;
}
static Ref<StyleBoxFlat> sb_expand(Ref<StyleBoxFlat> p_sbox, float p_left, float p_top, float p_right, float p_bottom) {