[canary] fails to install on BIOS system: dpkg-query: package 'grub-pc' is not installed

[Jean-Baptiste Lallement]

Canary Mantic 20230830

Installation in VM, BIOS, with network

Installation fails with
```
      curtin.util.ProcessExecutionError: Unexpected error while running command.
        Command: ['unshare', '--fork', '--pid', '--', 'chroot', '/target', 'dpkg-reconfigure', 'grub-pc']
        Exit code: 1
        Reason: -
        Stdout: ''
        Stderr: dpkg-query: package 'grub-pc' is not installed and no information is available
                Use dpkg --info (= dpkg-deb --info) to examine archive files.
                /usr/sbin/dpkg-reconfigure: grub-pc is not installed
```

Installation is successful on UEFI.

[Michael Hudson-Doyle (mwhudson)]

curtin side fix https://code.launchpad.net/~mwhudson/curtin/+git/curtin/+merge/450218

[Dan Bungert (dbungert)]

merged on curtin and subiquity

[Dan Bungert (dbungert)]

Injecting this into the test iso reveals problems installing grub-pc. Either grub-pc needs to be on the pool, or already in a layer.

[Jean-Baptiste Lallement (jibel)]

Installation fails with latest subiquity from u-d-i 1219 in candidate and image 20230831

[Dan Bungert (dbungert)]

Retested with 20230831.7 iso, this is resolved.