If a modifier key like ^ ´ or ¨ is active (even if it hit before launching Godot) physical keycode output gets corrupted

### Tested versions

- Reproducible in 4.3

### System information

Windows 11 - Godot 4.3 stable

### Issue description

Keyboards in some regions have keys that when pressed do nothing until you press a second key.
As an example hitting "¨" and then "A" results in "Ä". ^ + A = Â etc.

"event.get_physical_keycode()" is applying said modifiers to all of it's output, if one is currently active.

Here's my test script:
```gdscript
extends Node

func _ready() -> void:
var actions: = InputMap.get_actions()
for action in actions:
var events: Array[InputEvent] = InputMap.action_get_events(action)
for event in events:
if (event is InputEventKey):
var keycode : Key = event.get_physical_keycode()
var physical_label: = DisplayServer.keyboard_get_label_from_physical(keycode)
var key_name: = OS.get_keycode_string(physical_label)
print(key_name)
```

It normally prints:
```
key_name: A
key_name: B
key_name: C
key_name: D
key_name: E
key_name: F
key_name: G
```

But if I hit ¨ key before launching the project:
```
key_name: Ä
key_name: ¨
key_name: ¨
key_name: ¨
key_name: Ë
key_name: ¨
key_name: ¨
```

To clarify: That's the entire script. No _input() is involved at all.

### Steps to reproduce

Have keyboard with a modifier key like ¨, ´ or ^.

1. Hit said key once.
2. Launch the project.

### Minimal reproduction project (MRP)

[umlaut-caret-bug-test.zip](https://github.com/user-attachments/files/16830764/umlaut-caret-bug-test.zip)

Start with the attached minimal reproduction project and reproduce the issue by pressing ¨, ´, or ^ before launch. Trace InputEventKey.get_physical_keycode() and DisplayServer.keyboard_get_label_from_physical() on Windows, then verify that physical labels remain unaffected by an active dead key and that the sample output returns the expected A–G values.

Written by the indexing model from the issue text.