ci: check for failed services after boot

This should, hopefully, catch issues like systemd/systemd#21671
automagically.

test/mkosi-check-and-shutdown.service

@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+[Unit]
+Description=Check if any service failed and then shutdown the machine
+After=multi-user.target network-online.target
+Requires=multi-user.target
+Wants=systemd-resolved.service systemd-networkd.service network-online.target
+OnFailure=poweroff.target
+OnFailureJobMode=replace-irreversibly
+
+[Service]
+Type=oneshot
+ExecStartPre=-rm -f /failed-services
+ExecStart=/usr/lib/systemd/mkosi-check-and-shutdown.sh
+ExecStartPost=systemctl poweroff --no-block

test/mkosi-check-and-shutdown.sh

@@ -0,0 +1,9 @@
+#!/bin/bash -eux
+# SPDX-License-Identifier: LGPL-2.1-or-later
+
+systemctl --failed --no-legend | tee /failed-services
+
+# Exit with non-zero EC if the /failed-services file is not empty (we have -e set)
+[[ ! -s /failed-services ]]
+
+: >/testok