tests: Fix weird error on centos-9

centos-9 unit test sometimes fails with:

	=== RUN   TestPodSkipDevicesUpdate
	    systemd_test.go:114: container stderr not empty: basename: missing operand
	        Try 'basename --help' for more information.
	--- FAIL: TestPodSkipDevicesUpdate (0.11s)

I'm not sure why the container output is an error in basename. It seems
likely that the bashrc in that distro is kind of broken. Let's just run
a sleep command and forget about bash.

Signed-off-by: Rodrigo Campos <rodrigoca@microsoft.com>
(cherry picked from commit 4d0a60ca7f)
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/systemd/systemd_test.go

@@ -127,7 +127,7 @@ func TestPodSkipDevicesUpdate(t *testing.T) {
 
 	// Create a "container" within the "pod" cgroup.
 	// This is not a real container, just a process in the cgroup.
-	cmd := exec.Command("bash", "-c", "while true; do echo > /dev/null; done")
+	cmd := exec.Command("sleep", "infinity")
 	cmd.Env = append(os.Environ(), "LANG=C")
 	var stderr bytes.Buffer
 	cmd.Stderr = &stderr