pkg/cgroups: do not log ENOENT for Stat()

[Luap99]

This is flaking in podman for a while[1], likely ever since we enabled parallel tests. The cgroups may be removed while we try to gather stats, that is normal and expected and should not lead to warnings.

If no cgroup is found we still return ErrStatCgroup so a caller can then match this. There was attempt to fix this in podman[2] but we missed that the warning is printed here.

Example output from the test:
$ podman stats -a --no-stream --no-reset
time="2025-04-10T06:24:16-05:00" level=warning msg="Failed to retrieve cgroup stats: open /sys/fs/cgroup/user.slice/user-6259.slice/user@6259.service/user.slice/user-libpod_pod_6c6a40019844d59a70070655263388f2e81a04e2764a1cc138b37d8202e1fefe.slice/libpod-655275f1c204008257f81ebe2503557ffadaa210f988b2d15c1cc818160af72a.scope/memory.stat: no such file or directory" time="2025-04-10T06:24:16-05:00" level=warning msg="Failed to retrieve cgroup stats: open /sys/fs/cgroup/user.slice/user-6259.slice/user@6259.service/user.slice/user-libpod_pod_6c6a40019844d59a70070655263388f2e81a04e2764a1cc138b37d8202e1fefe.slice/libpod-655275f1c204008257f81ebe2503557ffadaa210f988b2d15c1cc818160af72a.scope/pids.current: no such file or directory"
ID NAME CPU % MEM USAGE / LIMIT MEM % NET IO BLOCK IO PIDS CPU TIME AVG CPU %
812b76331dbb a8bc9aac52b7-service 3.99% 0B / 4.092GB 0.00% 0B / 0B 0B / 0B 1 7.311ms 3.99%
...

[1] https://api.cirrus-ci.com/v1/artifact/task/5931471380152320/html/sys-podman-fedora-41-rootless-host-sqlite.log.html
[2] containers/podman@1f44d0f

Summary by Sourcery

Bug Fixes:

• Remove warning log when encountering a non-existent cgroup during stats retrieval, as this is an expected scenario during parallel tests

[sourcery-ai]

Reviewer's Guide by Sourcery

The pull request removes the logging of a warning message when the cgroup stats retrieval fails due to a non-existent file (ENOENT error). This change is made to prevent unnecessary warnings in scenarios where cgroups are expected to be removed during parallel tests, which is a normal and expected behavior.

No diagrams generated as the changes look simple and do not need a visual representation.

File-Level Changes

Change	Details	Files
Remove logging of ENOENT error in cgroup stats retrieval.	Deleted the log statement that logs a warning when a cgroup stat retrieval fails due to a non-existent file.	pkg/cgroups/cgroups_linux.go

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[Luap99]

cc @giuseppe

[sourcery-ai]

Hey @Luap99 - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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[vrothberg]

LGTM

[giuseppe]

/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: giuseppe, Luap99, sourcery-ai[bot], vrothberg

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• OWNERS [Luap99,giuseppe,vrothberg]

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