Severity: serious
Justification: non-declared dependency; fails on systemd upgrades if procps is missing

Dear Maintainer,

I have been see has been causing this issue all over jobs on Debian
CI: when upgrading from testing, it causes the apt upgrade to fail like
this:
----------------8<----------------8<----------------8<-----------------
Setting up systemd (262~rc1-2) ...
Can't exec "kill": No such file or directory at /usr/bin/deb-systemd-invoke line 179.
Job for systemd-journald.service failed because the control process exited with error code.
See "systemctl status systemd-journald.service" and "journalctl -xeu systemd-journald.service" for details.
Job for systemd-networkd.service failed because the control process exited with error code.
See "systemctl status systemd-networkd.service" and "journalctl -xeu systemd-networkd.service" for details.
Setting up systemd-resolved (262~rc1-2) ...
Could not execute systemctl:  at /usr/bin/deb-systemd-invoke line 148.
----------------8<----------------8<----------------8<-----------------

I can reproduce this locally with autopkgtest, like this:

autopkgtest --no-built-binaries --apt-upgrade --add-apt-release=unstable --pin-packages=unstable=src:systemd debian-security-support  -- incus autopkgtest/debian/testing/arm64

This is caused by an implicit dependeny on procps (for /usr/bin/kill).
The code around deb-systemd-invoke line 179 is:

178     if ($is_system) {
179         system('kill', '-s', $signal, '1');
180     } else {
181         system('systemctl', '--quiet', 'kill', '--kill-whom=main', '--signal', $signal, 'user@*.servic    e');
182     }

The attached patch (against git master) fixes the issue, i.e. if I have
the package with this patch installed, then upgrading systemd works.