Does the unintentional failure of the big toe of the left foot to touch the ground between the two prostrations affect the validity of the prayer?

We have previously detailed the prescribed posture for sitting during the Tashahhud, and the matter is broad. Any sitting posture is sufficient, and your prayer is valid. Imam An-Nawawi said: "There is no specific posture for sitting in these instances that is obligatory for sufficiency; rather, any way one sits is sufficient... However, the Sunnah is tawarruk in the final part of the prayer and iftirash in other parts." Your prayer is valid, and there is no blame upon you.