Editor freezes when unable to open a file in external file manager

### Tested versions

v4.4.1.stable.nixpkgs [49a5bc7b6]

### System information

Godot v4.4.1.stable (49a5bc7b6) - cpe:/o:nixos:nixos:25.11 #1-NixOS SMP PREEMPT_DYNAMIC Thu Jul 17 16:37:24 UTC 2025 on Wayland - X11 display driver, Multi-window, 2 monitors - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3070 (nvidia; 570.172.08) - AMD Ryzen 5 5600X 6-Core Processor (12 threads)

Also, my default external file manager, according to `xdg-mime query default inode/directory`, is [yazi](https://github.com/sxyazi/yazi).

### Issue description

#### What Happens
The editor freezes.

#### What I Would Expect to Happen
Either the editor issues some kind of warning ("Unable to open external file manager!") and continues running, or the external file manager is opened successfully (this is how it behaves on Windows).

### Steps to reproduce

1. Right click a file in the FileSystem
2. Click "Show in File Manager"

### Minimal reproduction project (MRP)

N/A

Start at the FileSystem panel's “Show in File Manager” action and reproduce the freeze on NixOS with yazi configured as the default file manager. Trace the external file-manager launch path and verify that the editor either opens the manager or reports failure without freezing.

Written by the indexing model from the issue text.