### 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)






RS::get_singleton()->canvas_item_set_parent(onion.capture.canvas_item, onion.capture.canvas);
	onion.capture.material.instantiate();
	onion.capture.shader.instantiate();
	onion.capture.shader->set_code(R"(
// Animation editor onion skinning shader.
shader_type canvas_item;
uniform vec4 bkg_color;
uniform vec4 dir_color;
uniform bool differences_only;
uniform sampler2D present;
float zero_if_equal(vec4 a, vec4 b) {
	return smoothstep(0.0, 0.005, length(a.rgb - b.rgb) / sqrt(3.0));
}
void fragment() {
	vec4 capture_samp = texture(TEXTURE, UV);
	float bkg_mask = zero_if_equal(capture_samp, bkg_color);
	float diff_mask = 1.0;
	if (differences_only) {
		// FIXME: If Y-flips across render target, canvas item, etc. was handled correctly,
		//        this would not be as convoluted in the shader.
		vec4 capture_samp2 = texture(TEXTURE, vec2(UV.x, 1.0 - UV.y));
		vec4 present_samp = texture(present, vec2(UV.x, 1.0 - UV.y));
		diff_mask = 1.0 - zero_if_equal(present_samp, bkg_color);
	}
	COLOR = vec4(capture_samp.rgb * dir_color.rgb, bkg_mask * diff_mask);
}
)");
	RS::get_singleton()->material_set_shader(onion.capture.material->get_rid(), onion.capture.shader->get_rid());
}
AnimationPlayerEditor::~AnimationPlayerEditor() {