lxc-ci: Debian 11: `login -f` slow

On debian/11/amd64, login -f john takes a few seconds to start a shell whereas sudo --login --user john works instantly.

The following information is found in the log files:

[Sep 1 13:04] audit: type=1400 audit(1630501469.294:114): apparmor="DENIED" operation="mount" info="failed flags match" error=-13 profile="lxd-d11_</var/lib/lxd>" name="/run/systemd/unit-root/" pid=6310 comm="(d-logind)" flags="ro, remount, noatime, bind"
[  +0.016474] audit: type=1400 audit(1630501469.310:115): apparmor="DENIED" operation="mount" info="failed flags match" error=-13 profile="lxd-d11_</var/lib/lxd>" name="/run/systemd/unit-root/" pid=6330 comm="(d-logind)" flags="ro, remount, noatime, bind"
[  +0.017953] audit: type=1400 audit(1630501469.330:116): apparmor="DENIED" operation="mount" info="failed flags match" error=-13 profile="lxd-d11_</var/lib/lxd>" name="/run/systemd/unit-root/" pid=6350 comm="(d-logind)" flags="ro, remount, noatime, bind"
[  +0.016828] audit: type=1400 audit(1630501469.346:117): apparmor="DENIED" operation="mount" info="failed flags match" error=-13 profile="lxd-d11_</var/lib/lxd>" name="/run/systemd/unit-root/" pid=6370 comm="(d-logind)" flags="ro, remount, noatime, bind"
[  +0.017574] audit: type=1400 audit(1630501469.362:118): apparmor="DENIED" operation="mount" info="failed flags match" error=-13 profile="lxd-d11_</var/lib/lxd>" name="/run/systemd/unit-root/" pid=6398 comm="(d-logind)" flags="ro, remount, noatime, bind"