menu toggle: Split button checkbox has no padding

[andrew-ronaldson]

In this example on the React tab of staging there is an inline style that uses a broken spacer variable.

Short-term we could just update from padding-left:var(--pf-v5-global--spacer--sm) to padding-inline-start: var(--pf-t--global--spacer--gap--action-to-action--plain)

Long-term this doesn't exist on the Core examples. This should be updated so we don't need custom inline styling