cryptsetup-close fails because xdg-desktop-portal is using the disk

### What Happened?

I have this LUKS-encrypted removable disk that I usually mount like this:

```sh
sudo cryptsetup open /dev/sdb mybackup
sudo mount /dev/mapper/mybackup /mnt/backup
```

Then I use elementary Files to browse it.

To eject it, first I close Files and any other app running in the foreground that could be using it, and then:

```sh
sudo umount /mnt/backup
sudo cryptsetup close mybackup
```

Unfortunately, the `cryptsetup close` command fails with "Device is still in use".

#### Workarounds

The easiest way around it is to **log out of my user**, supposedly because it kills whatever user processes are accessing the disk.

To find out what exactly is using it, I used `fuser -m /dev/mapper/mybackup`, which gave me one PID. The process is `/usr/libexec/xdg-desktop-portal`, owned by my user; and apparently it is managed by the `xdg-desktop-portal.service` (in `--user` scope).

Restarting the systemd service allows me to close the LUKS device:

```sh
systemctl restart --user xdg-desktop-portal.service
sudo cryptsetup close mybackup
```

I don't know how this service works, but I can see in `systemctl status --user` that elementary Files is somehow connected to it:

```
● helium
State: running
Units: 575 loaded (incl. loaded aliases)
Jobs: 0 queued
Failed: 0 units
Since: Thu 2026-02-12 09:21:34 -03; 8h ago
systemd: 255.4-1ubuntu8.12
CGroup: /user.slice/user-1000.slice/user@1000.service
├─app.slice
│ ├─_io.elementary.files.xdg-desktop-portal.service
│ │ └─3684 /usr/lib/x86_64-linux-gnu/io.elementary.files.xdg-desktop-portal
│ ├─_io.elementary.settings-daemon.xdg-desktop-portal.service
│ │ └─3582 /usr/libexec/io.elementary.settings-daemon.xdg-desktop-portal
```

### Steps to Reproduce

Follow my steps described above.

Observations:
- The device I'm using is a flash stick containing a single partition that is encrypted with LUKS (without LVM). The unlocked device contains an _ext4_ filesystem.
- The problem doesn't happen all the time. I have yet to figure out how to reliably reproduce it.
- Other apps that I use to access files from that disk: GNOME Loupe (image viewer), mpv (video player) and elementary Code for text files. I always close them all when I'm done.

### Expected Behavior

Device should not be kept busy when no apps in the foreground are using it.

### OS Version

8.x (Circe)

### OS Architecture

amd64 (on most hardwares)

### Session Type

Secure Session (Wayland, This is the default)

### Software Version

Latest release (I have run all updates)

### Log Output

```shell

```

### Hardware Info

_No response_