add missing import

Author: fchapoton

src/sage/combinat/posets/posets.py

@@ -7319,6 +7319,7 @@ def apozeta_polynomial(self):
             sage: parent(_)
             Univariate Polynomial Ring in q over Rational Field
         """
+        from sage.functions.other import binomial
         R = PolynomialRing(QQ, 'q')
         q = R.gen()