[DO-NOT-MERGE] Test pid cgroup join issue flake

This PR is just for testing and verification related to the issue #1196

Signed-off-by: vikaschoudhary16 <choudharyvikas16@gmail.com>

vendor/github.com/opencontainers/runc/libcontainer/cgroups/systemd/apply_systemd.go

@@ -288,6 +288,9 @@ func (m *Manager) Apply(pid int) error {
 		}
 	}
 
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
 	if _, err := theConn.StartTransientUnit(unitName, "replace", properties, nil); err != nil && !isUnitExists(err) {
 		return err
 	}