Unmounting a mount containing a file being edited by Code does not result in a "busy" warning

### What Happened?

Unmounting a mount containing a file being edited by Code does not result in a "busy" warning

### Steps to Reproduce

1. Mount e.g. a USB stick
2. Open a text file on that mount with Code
3. Ensure "Save files when changed" s OFF
4. Make some changes
5. Unmount the mount using Files (latest source)
6. No warning is given that the mount is in use by Code

### Expected Behavior

A user might expect to get a warning in this situation (although other text editors do not hold files open on the mount under similar circumstances either).

Fortunately Code handles the situation gracefully and gives the user the opportunity to save the file elsewhere or remount.

The desired behaviour is uncertain and suggestions are invited.

### OS Version

8.x (Circe)

### OS Architecture

amd64 (on most hardwares)

### Session Type

Secure Session (Wayland, This is the default)

### Software Version

Early Access or Compiled from git

### Log Output

```shell

```

### Hardware Info

_No response_

First reproduce the scenario using Files and Code with an unsaved file on the mounted USB stick. Clarify whether a warning is required, then identify the unmount-warning entry point and define completion around the agreed behavior and a regression test.

索引モデルが issue の本文から書いたものです。