[MINOR] Dieresis not working from my keyboard

### Tested versions

4.2.2.stable

### System information

Windows 7 - Godot 4.2.2 - Microsoft Wired Keyboard 600 (Mouse and Keyboard Center) (Azerty layout)

### Issue description

Never thought I would fall one day on a minor bug of that sort of thing, but figuring out it was an Engine bug (or maybe not, after all can be a keyboard/computer issue since I have no way to check) was frustating, especially for something so oddly specific.

So disclaimer : That a minor bug. A very minor thing, and honestly not even sure that a real thing.

That said, whats the bug : Every letter comporting dieresis will not write using the standard method on my keyboard meaning SHIFT+"^", but I can copy paste it, I can type it with a virtual keyboard. "Where ?", well both in-editor and in-game.

It's not a font problem for in-game cuz I can copy paste it fine, it's not a keyboard problem cuz I can just type it elsewhere, unless there some very specific problem with Godot ???

Well something else to note, is that normally typing a character that cannot have accent will just type the accent alone and that another character with it right ? So if you type twice that accent it will type it twice ? Well if I do that in Godot with dieresis, which I'll put it again, for me it's SHIFT+"^", will do : `` ^¨ `` ????

Whatever that nonsense is.

### Steps to reproduce

Either you can reproduce by typing it, but that probably not the case, else I guess it would have been reported before, so I guess do it with an AZERTY keyboard... Else... I have honestly no fucking idea.

### Minimal reproduction project (MRP)

.

No files or tests are named. First reproduce the issue in Godot 4.2.2 on Windows 7 with an AZERTY keyboard, checking both the editor and a running project; compare dead-key input for dieresis with copy-pasted text and virtual-keyboard input. Done means the character can be entered normally or the limitation is documented with a confirmed cause.

Written by the indexing model from the issue text.