Yawning is a common sign of tiredness, though people yawn for other reasons. The causes of yawning are not well understood (See wikipedia).
There is no direct mention of yawning in the Bible (Ps 5 : 9 is sometimes mentioned, but it’s clear that “their throat is an open grave” is not about yawning).
The ground “yawned” in a particularly dramatic way for Korah, Dathan, and Abiram:
And the earth opened its mouth and swallowed them up, with their households and all the people who belonged to Korah and all their goods. (Num 16:32)
But this is more about swallowing than yawning (and you can’t do both at once).
Yawning is often a sign of sleepiness, and the Bible has much to say about that. For example:
A little sleep, a little slumber, a little folding of the hands to rest, and poverty will come upon you like a robber, and want like an armed man. (Pro 24:33-34)