### Godot version

4.2.beta.custom_build [51f81e1c8]

### System information

macOS 11.0+

### Issue description

I could sense a recent merging of a few pull requests on here:

<img width="865" alt="image" src="https://github.com/godotengine/godot/assets/1129695/1cf7d144-a4d2-4514-abca-1405222e702a">

This bug has the following related merges as the most recent ones:

https://github.com/godotengine/godot/pull/80813
https://github.com/godotengine/godot/pull/80939

The pull requests are for reviving onion-skinning capabilities, but this causes a minor unexpected result (see Steps to reproduce)



### Steps to reproduce

## A. Use 4.2.beta.custom_build [51f81e1c8]

1. Obtain the attached minimal reproduction project
2. Select the AnimationPlayer node
<img width="1468" alt="image" src="https://github.com/godotengine/godot/assets/1129695/ca16d7a6-7690-45b4-b8f9-b12fded64ca4">
3. In the Animation panel, click "Edit" to find your shortcuts for "Go to Next Step" and "Go to Previous Step"
<img width="410" alt="image" src="https://github.com/godotengine/godot/assets/1129695/a708e196-2eb9-42ea-bf0e-fd0aa88a9e60">
4. Use the shortcuts to spam go back and forth the animation

Expected result: animation goes smoothly

https://github.com/godotengine/godot/assets/1129695/c24c498c-7f77-4cc9-a1c9-a1627d89c58b



Actual result: animation jumps crazily


https://github.com/godotengine/godot/assets/1129695/947bf5b4-a0ab-42d4-bb5b-201800b4bdc6


https://github.com/godotengine/godot/assets/1129695/65303cd0-8c2d-4a35-9d16-c94752ac2e3a




## B. My successful yet unverified fix attempt on 4.2.beta.custom_build [51f81e1c8]

Either by:

<img width="831" alt="image" src="https://github.com/godotengine/godot/assets/1129695/80d167ae-27e7-4ec4-a4c9-ffc7adc0353f">


Or by:

<img width="806" alt="image" src="https://github.com/godotengine/godot/assets/1129695/2bae8697-8ef3-48dc-9f0a-2b5fe568ed43">


I don't see any negative impact on Onion Skinning or other functions by the above fix attempt, but I am not sure, I need someone to help me verify this.



### Minimal reproduction project

[gd_anim_unittest_1.zip](https://github.com/godotengine/godot/files/12909805/gd_anim_unittest_1.zip)






if (!onion.can_overlay) {
		return;
	}
	
	if (!_are_onion_layers_valid()) {
		return;
	}
	RID ci = p_overlay->get_canvas_item();
	Rect2 src_rect = p_overlay->get_global_rect();
	
	src_rect.position.y = onion.capture_size.y - (src_rect.position.y + src_rect.size.y);
	src_rect.size.y *= -1;
	Rect2 dst_rect = Rect2(Point2(), p_overlay->get_size());
	float alpha_step = 1.0 / (onion.steps + 1);
	uint32_t capture_idx = 0;
	if (onion.past) {
		float alpha = 0.0f;
		do {
			alpha += alpha_step;
			if (onion.captures_valid[capture_idx]) {
				RS::get_singleton()->canvas_item_add_texture_rect_region(
						ci, dst_rect, RS::get_singleton()->viewport_get_texture(onion.captures[capture_idx]), src_rect, Color(1, 1, 1, alpha));