Test failures on Ubuntu containers (`no cgroup mount found in mountinfo`)

Hello, some tests are failing when building new version under Ubuntu.
I can presume that systemd is not installed into the build environment, but maybe it is shown as running because it runs on the host?
https://launchpadlibrarian.net/827407202/buildlog_ubuntu-resolute-amd64.golang-github-opencontainers-cgroups_0.0.4-2_BUILDING.txt.gz

=== RUN TestInvalidCgroupPath
paths_test.go:19: couldn't get cgroup root: no cgroup mount found in mountinfo
--- FAIL: TestInvalidCgroupPath (0.00s)
=== RUN TestTryDefaultCgroupRoot
paths_test.go:102: tryDefaultCgroupRoot: want "/sys/fs/cgroup", got ""
--- FAIL: TestTryDefaultCgroupRoot (0.00s)
=== RUN TestPidsSetMax
--- PASS: TestPidsSetMax (0.00s)
=== RUN TestPidsSetUnlimited
--- PASS: TestPidsSetUnlimited (0.00s)
=== RUN TestPidsStats
--- PASS: TestPidsStats (0.00s)
=== RUN TestPidsStatsUnlimited
--- PASS: TestPidsStatsUnlimited (0.00s)
FAIL
FAIL github.com/opencontainers/cgroups/fs 0.075s
=== RUN TestParseCgroupFromReader
--- PASS: TestParseCgroupFromReader (0.00s)
=== RUN TestDefaultDirPath
defaultpath_test.go:52: need cgroupv2

? github.com/opencontainers/cgroups/internal/path [no test files]
=== RUN TestNilResources
manager_test.go:40: no cgroup mount found in mountinfo
--- FAIL: TestNilResources (0.00s)
=== RUN TestNilResourcesSystemd
manager_test.go:24: requires systemd
--- SKIP: TestNilResourcesSystemd (0.00s)
FAIL
FAIL github.com/opencontainers/cgroups/manager 0.004s
=== RUN TestRangeToBits

Start with the failing tests in paths_test.go, defaultpath_test.go, and manager_test.go, then inspect the linked Ubuntu build log to understand the missing cgroup mount and systemd environment. Reproduce the failures in an Ubuntu container and make the affected test behavior match environments without those mounts; done means the relevant test suites pass or correctly handle the reported environment.