Really called that post credits scene.
“Listen to your inner voice.”
That’s a good joke throughout Toy Story 4, Buzz using his voice box as an inner voice. But it also kind of set up the end of the movie when he tells Woody that Bonnie will be ok without him.
Side Note: It was pretty obvious for Buzz and Woody to end the franchise by saying the four words that we all have known since the first film. They couldn’t not do that.