Bug#1052058: apt: refuses to downgrade itself to a version that works on the system

[Philippe Grégoire <from-debian@infose.cz>]

Hi,

I'm being hit hard by this at the moment. Context:

```
# apt --version
apt 2.7.5 (amd64)

# apt-get autoremove
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following packages will be REMOVED:
  libavcodec59 libavdevice59 libavfilter8 libavformat59 libavutil57 libmfx1 libplacebo208 libpostproc56 libspice-server1 libswscale6 tzdata-legacy
0 upgraded, 0 newly installed, 11 to remove and 15 not upgraded.
E: /bin resolved to a different inode than /usr/bin
E: Unmerged usr is no longer supported, install usrmerge to continue.
N: See https://www.debian.org/releases/bookworm/amd64/release-notes/ch-information.en.html#a-merged-usr-is-now-required for more details.

# mount | grep -E ' (/|/usr) '
/dev/mapper/vg.x-root on / type ext4 (rw,noatime)
/dev/mapper/vg.x-usr on /usr type ext4 (rw,noatime)

# dpkg -l usrmerge | grep ^ii
ii  usrmerge       37           all          Convert the system to the merged /usr directories scheme
```

As such, I can no longer install or remove packages since my system is partitioned. I'd like to point out that the above link does not specifically mention disk partitioning, but only how files are placed on disk.

Obviously, re-partitioning the system is something I'd like to avoid at the moment.

Thinking about it, in the long term, due to the merge and how packagers are expected to be able to address files (e.g. /bin/sh vs /usr/bin/sh), I don't see any other way than re-partitioning. Re-partitioning will be done by a future me.

Regards,

P.S. I'm uncertain why /lib isn't also merged with /usr/lib