That's rather irrelevant, the Soviets also had an alliance with the Czechs, this one did not require any outside nation's approval to activate, and it was one which the Soviets seemed eager to honor. So this would be a legal avenue to circumvent the requirements that Italy or Britain approve. But never mind the fact that Stalin does not need a legal loophole to help the Czechs if he wants to if the Germans invaded.
So if the French and Czechs stand and fight, it's likely The Soviets get involved, if anything then just to eliminate the German strategic and ideological threat before it grows too powerful. Up until the Molotov-Ribbentrop pact Stalin expressed desire to work with the allies against Germany.
But how are the Soviets going to get involved? Neither Poland nor Romania are likely to invite them in so there is no route for them to reach Germany or Czechoslovakia.