Crash when unmounting cdrom

As shown below, we attempt to unmount the cdrom twice:

2022-09-20 08:35:59,483 DEBUG subiquitycore.utils:114 astart_command called: ['systemd-run', '--wait', '--same-dir', '--property', 'SyslogIdentifier=subiquity_log.1973', '--setenv', 'PATH=/snap/subiquity/x1/bin:/snap/subiquity/x1/usr/bin:/usr/local/sbin:/
usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/snap/subiquity/x1/bin:/snap/subiquity/x1/sbin', '--setenv', 'PYTHONPATH=:/snap/subiquity/x1/lib/python3.8/site-packages', '--setenv', 'PYTHON=/snap/subiquity/x1/usr/bin/pyt
hon3.8', '--setenv', 'SNAP=/snap/subiquity/x1', '--', 'umount', '/target/cdrom']
[...]
2022-09-20 08:36:04,159 DEBUG subiquitycore.utils:114 astart_command called: ['systemd-run', '--wait', '--same-dir', '--property', 'SyslogIdentifier=subiquity_log.1973', '--setenv', 'PATH=/snap/subiquity/x1/bin:/snap/subiquity/x1/usr/bin:/usr/local/sbin:/
usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/snap/subiquity/x1/bin:/snap/subiquity/x1/sbin', '--setenv', 'PYTHONPATH=:/snap/subiquity/x1/lib/python3.8/site-packages', '--setenv', 'PYTHON=/snap/subiquity/x1/usr/bin/pyt
hon3.8', '--setenv', 'SNAP=/snap/subiquity/x1', '--', 'umount', '/target/cdrom']

We do it once explicitly and then a second time in the self.cleanup() method.

        await self.unmount(
                Mountpoint(mountpoint=target_mnt.p('cdrom')),
                remove=False)
        os.rmdir(target_mnt.p('cdrom'))

        await _restore_dir('etc/apt')

        if self.app.base_model.network.has_network:
            await run_curtin_command(
                self.app, context, "in-target", "-t", target_mnt.p(),
                "--", "apt-get", "update", private_mounts=True)
        else:
            await _restore_dir('var/lib/apt/lists')

        await self.cleanup()

https://github.com/canonical/subiquity/pull/1429

We believe this issue has been resolved in Subiquity 23.04.2.

If you had tested this with a pre-final version of Ubuntu 23.04, it's
recommended to download the final install media.

For testing with Ubuntu Server 22.04.x or 20.04.x, when running
Subiquity, you should offered a new version of the installer. Please
take that update to version 23.04.2 or later to get the fix.

If this is still a problem for you, please make a comment and set the state
back to New. Thank you for the bug report.