Equal event names cause the modron to halt even though not fixpoint

[dvaergiller]

If two states in a modron inject the same event (e.g. skip), mechanus will consider the modron to be on a fixpoint (not progressing) even though the state has changed and the modron will halt.

This can cause premature halting of the modron. See:
https://github.com/kivra/mechanus_fsm/blob/master/src/mechanus_modron.erl#L74