Steam client breaks Godot X11

### Tested versions

v4.6.stable.official [89cea1439]

### System information

linux, x11, arch, awesome

### Issue description

When I launch the game and then start Steam for testing, I get X11 errors. This likely happens due to focus differences, and Godot was expecting something else. I am also using GodotSteam, but I don’t see this as its specific problem.

### Steps to reproduce

```
ERROR: Unhandled XServer error: BadWindow (invalid Window parameter)
Major opcode of failed request: 18
Serial number of failed request: 0
Current serial number in output stream: 360789
at: default_window_error_handler (platform/linuxbsd/x11/display_server_x11.cpp:1310)
ERROR: Unhandled XServer error: BadWindow (invalid Window parameter)
Major opcode of failed request: 25
Serial number of failed request: 0
Current serial number in output stream: 360790
at: default_window_error_handler (platform/linuxbsd/x11/display_server_x11.cpp:1310)
ERROR: Unhandled XServer error: BadWindow (invalid Window parameter)
Major opcode of failed request: 18
Serial number of failed request: 0
Current serial number in output stream: 360805
at: default_window_error_handler (platform/linuxbsd/x11/display_server_x11.cpp:1310)
ERROR: Unhandled XServer error: BadWindow (invalid Window parameter)
Major opcode of failed request: 25
Serial number of failed request: 0
Current serial number in output stream: 360806
at: default_window_error_handler (platform/linuxbsd/x11/display_server_x11.cpp:1310)
```

From what I can tell, these errors occur in response to Steam creating windows when it launches, and Godot has nothing to do with it, but reports the errors as a reaction. After the Steam client finishes loading, Godot stabilizes.

### Minimal reproduction project (MRP)

I think even a blank project with a window + opening the Steam client would reproduce it.

Start with platform/linuxbsd/x11/display_server_x11.cpp around default_window_error_handler at line 1310, then reproduce the report using a blank project and Steam on Linux/X11. Trace the BadWindow errors while Steam creates windows and determine the expected behavior; done means the issue is resolved or clearly confirmed as an external X11/Steam condition without spurious Godot errors.

Written by the indexing model from the issue text.