Fix state/root bug in shim sandbox controller

[djdongjin]

Fix #11320

This is a shim-sandbox-controller side bug other than LoadExistingShims, as that function is also used in TaskManager and it passes the dirs correctly:

containerd/core/runtime/v2/task_manager.go

Line 75 in 8efbc01

root, state := ic.Properties[plugins.PropertyRootDir], ic.Properties[plugins.PropertyStateDir]

containerd/core/runtime/v2/task_manager.go

Line 81 in 8efbc01

return NewTaskManager(ic.Context, root, state, shimManager)

containerd/core/runtime/v2/task_manager.go

Lines 97 to 98 in 8efbc01

	func NewTaskManager(ctx context.Context, root, state string, shims *ShimManager) (*TaskManager, error) {
	if err := shims.LoadExistingShims(ctx, state, root); err != nil {

[djdongjin]

fyi @mxpv @abel-von PTAL when you have some time. thank you!