Crash when renaming in the thumbnail panel conflicts with another file

[SaracenOne]

Godot version

5dc10b5

System information

Windows 11

Issue description

The engine crash if you attempt to rename a file in the thumbnail file browser to the same name as a file which already exists.

Steps to reproduce

Create two files in the Godot file browser.
In the thumbnail view, press F2 or right click and select rename on one of them.
Name this file to the same filename as the other file.
The engine will now crash.

Minimal reproduction project

N/A