Bug 501948

### Bug Description

While [upgrading the FreeCAD snap to `core24`](https://github.com/FreeCAD/FreeCAD-snap/pull/169), and after the latest `kde-neon` fixes (https://github.com/canonical/snapcraft/pull/5261), the snap builds and runs successfully, but outputs quite a few warnings and an error on the terminal as detailed below.

Those don't seem to affect running FreeCAD, but I thought I'd file an issue just in case. At least the missing `command-chain/locale-gen` error sounds like a genuine bug.

### To Reproduce

1. Install the FreeCAD snap available for testing as an [artifact on the last workflow run page](https://github.com/furgo16/FreeCAD-snap/actions/runs/13558406862).
2. Run `freecad` on the terminal and watch the output while starting the app.

### Environment

Snapcraft on Ubuntu 24.04 LTS, snap built on GitHub CI using destructive mode

### snapcraft.yaml

```yaml
https://github.com/FreeCAD/FreeCAD-snap/blob/37d742422ea3f4240a7acf8ce3725e48bde328a6/snap/snapcraft.yaml
```

### Relevant log output

```shell
update.go:85: cannot change mount namespace according to change mount (/snap/gtk-common-themes/1535/share/gtk2/Materia-compact /snap/freecad/x1/data-dir/themes/Materia-compact-2 none bind,ro 0 0): cannot write to "/snap/gtk-common-themes/1535/share/gtk2/Materia-compact" because it would affect the host in "/snap"
update.go:85: cannot change mount namespace according to change mount (/snap/gtk-common-themes/1535/share/gtk2/Materia-dark-compact /snap/freecad/x1/data-dir/themes/Materia-dark-compact-2 none bind,ro 0 0): cannot write to "/snap/gtk-common-themes/1535/share/gtk2/Materia-dark-compact" because it would affect the host in "/snap"
update.go:85: cannot change mount namespace according to change mount (/snap/gtk-common-themes/1535/share/gtk2/Yaru-MATE-dark /snap/freecad/x1/data-dir/themes/Yaru-MATE-dark-2 none bind,ro 0 0): cannot use "/snap/gtk-common-themes/1535/share/gtk2/Yaru-MATE-dark" as bind-mount source: not a directory
update.go:85: cannot change mount namespace according to change mount (/snap/gtk-common-themes/1535/share/gtk2/Yaru-MATE-light /snap/freecad/x1/data-dir/themes/Yaru-MATE-light-2 none bind,ro 0 0): cannot use "/snap/gtk-common-themes/1535/share/gtk2/Yaru-MATE-light" as bind-mount source: not a directory
/snap/freecad/x1/kf5/snap/command-chain/desktop-launch: line 23: /snap/freecad/x1/snap/command-chain/locale-gen: No such file or directory
ERROR: /snap/freecad/x1/snap/command-chain/locale-gen exited abnormally with status 127
```

### Additional context

- We're using the snapcraft `edge` channel to have the changes in https://github.com/canonical/snapcraft/pull/5261 to the `kde-neon` extension available.
- ScarlettGatelyMoore mentions: "locale-gen is no longer needed in core24, looks like I need to fix kf5 in snapcraft-desktop-integration. The mount errors I am not sure of."