The short answer
Yes to the flesh, but never the pit — cherry stones are toxic.
Why
Cherry flesh is a fine sweet treat, but the pit (stone) contains cyanide compounds, exactly like apple seeds and other stone-fruit pits. A budgie must never have access to the pit.
How to feed it
Remove the stem and pit completely, then offer a small piece of the flesh.
How much & how often
A small piece occasionally.