cross-testing essential packages fails

Maybe APT should not consider crossgrading a package as a removal and APT should be fixed instead of autopkgtest:

root@gg-libyaml:~# apt install gzip:i386
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  gcc-10-base gcc-10-base:i386 libatomic1 libc6:i386 libcc1-0 libcrypt-dev libcrypt1 libcrypt1:i386 libgcc-s1 libgcc-s1:i386 libgomp1 libidn2-0:i386 libitm1 liblsan0
  libquadmath0 libstdc++6 libtsan0 libubsan1 libunistring2 libunistring2:i386
Suggested packages:
  glibc-doc:i386 locales:i386
The following packages will be REMOVED:
  gzip
The following NEW packages will be installed:
  gcc-10-base:i386 gzip:i386 libc6:i386 libcrypt1:i386 libgcc-s1:i386 libidn2-0:i386 libunistring2:i386
The following packages will be upgraded:
  gcc-10-base libatomic1 libcc1-0 libcrypt-dev libcrypt1 libgcc-s1 libgomp1 libitm1 liblsan0 libquadmath0 libstdc++6 libtsan0 libubsan1 libunistring2
WARNING: The following essential packages will be removed.
This should NOT be done unless you know exactly what you are doing!
  gzip
14 upgraded, 7 newly installed, 1 to remove and 121 not upgraded.
Need to get 5303 kB of archives.
After this operation, 15.2 MB of additional disk space will be used.
You are about to do something potentially harmful.
To continue type in the phrase 'Yes, do as I say!'
 ?]
Abort.

We discussed that with @juliank and we agreed that APT should not let this cross-grading happen without confirmation at least thus the most generic fix would be in autopkgtest.

This continues to be an issue and one which I ran into recently:

runner/autopkgtest --setup-commands="dpkg --add-architecture i386; apt-get update" --architecture i386 gzip -- qemu --ram-size=4096 --cpus=4 /srv/vms/autopkgtest-lunar-amd64.img
...
Broken gzip:amd64 Conflicts on gzip:i386 < none -> 1.12-1ubuntu1 @un puN Ib >
  Considering gzip:i386 5103 as a solution to gzip:amd64 5103
  Removing gzip:amd64 rather than change gzip:i386
Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 gzip : Conflicts: gzip:i386 but 1.12-1ubuntu1 is to be installed
 gzip:i386 : Conflicts: gzip but 1.12-1ubuntu1 is to be installed
E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.
simple-gzip FAIL badpkg
blame: gzip
badpkg: Test dependencies are unsatisfiable. A common reason is that your testbed is out of date with respect to the archive, and you need to use a current testbed or run apt-get update or use -U.
autopkgtest [14:05:26]: @@@@@@@@@@@@@@@@@@@@ summary
simple-gzip FAIL badpkg
blame: gzip
badpkg: Test dependencies are unsatisfiable. A common reason is that your testbed is out of date with respect to the archive, and you need to use a current testbed or run apt-get update or use -U.
qemu-system-x86_64: terminating on signal 15 from pid 1828712 (/usr/bin/python3)