Shift + ui_accept does not work with pressed signal on button

### Tested versions

Godot v4.4.dev1
Godot v4.0.stable

### System information

Fedora Linux 40 (KDE Plasma) - Wayland - Vulkan (Forward+)

### Issue description

Shift + ui_accept (same with Ctrl, Alt) does not work with pressed signal on button when usign this code:

_This code works if you switch KEY_SHIFT to KEY_A_

```
func _on_pressed() -> void:
if Input.is_key_pressed(KEY_SHIFT):
print("Shift was pressed")
```

This works in Godot 3

### Steps to reproduce

connect pressed signal to a script
see code above
grab button focus
press shift + ui_accept
nothing is printed

### Minimal reproduction project (MRP)

[shift-and-accept-in-pressed.zip](https://github.com/user-attachments/files/16888279/shift-and-accept-in-pressed.zip)

Start with the attached shift-and-accept.zip minimal reproduction and reproduce the issue using the button's pressed signal, ui_accept, and Input.is_key_pressed(KEY_SHIFT). Trace the button activation and input handling entry points to compare modifier-key behavior with KEY_A and Godot 3; done means Shift, Ctrl, and Alt are observable when activating the focused button as described.

Written by the indexing model from the issue text.