Fix constant WARNING: No swap limit support on cgroup v2 hosts

[AkihiroSuda]

- What I did
Fix constant WARNING: No swap limit support on cgroup v2 hosts

Fix #43646

- How I did it

Replace cgroups.ParseCgroupFile with cgroups.ParseCgroupFileUnified:

• ParseCgroupFile: fix wrong comment about unified hierarchy ; add ParseCgroupFileUnified to get the unified path containerd/cgroups#232

- How to verify it
Run docker info on cgroup v2 hosts with support for memory.swap.max, and make sure WARNING: No swap limit support is not printed

- Description for the changelog

Fix constant WARNING: No swap limit support on cgroup v2 hosts

- A picture of a cute animal (not mandatory but encouraged)
🐧

[thaJeztah]

Failure in CI in TestExecWithPrivileged - wondering if it's related to #43647, as docker logs is involved;

=== RUN   TestDockerSuite/TestExecWithPrivileged
    docker_cli_exec_test.go:463: assertion failed: 
        Command:  /usr/local/cli/docker logs parent
        ExitCode: 1
        Error:    exit status 1
        Stdout:   Privileged exec has not run yet
        Privileged exec has not run yet
        Privileged exec has not run yet
        Privileged exec has not run yet
        Privileged exec has not run yet
        Privileged exec has not run yet
        Privileged exec has not run yet
        Privileged exec has not run yet
        Privileged exec has not run yet
        Privileged exec has not run yet
        Running exec --privileged
        Running exec --privileged
        Running exec --privileged
        
        Stderr:   mknod: /tmp/sda: Operation not permitted
        mknod: /tmp/sda: Operation not permitted
        error from daemon in stream: Error grabbing logs: invalid character ',' looking for beginning of object key string
        
        
        
        Failures:
        ExitCode was 1 expected 0
        Expected no error
    --- FAIL: TestDockerSuite/TestExecWithPrivileged (1.17s)

I gave CI a kick

[thaJeztah]

LGTM

[thaJeztah]

All green now 👍