src/sage/tests/benchmark.py: add "needs sage.libs.eclib"

One example in this file needs "needs sage.libs.eclib"

Author: orlitzky

src/sage/tests/benchmark.py

@@ -1635,7 +1635,7 @@ def sage(self):
 
             sage: from sage.tests.benchmark import EllipticCurveMW
             sage: B = EllipticCurveMW([1,2,3,4,5])
-            sage: isinstance(B.sage()[1], float)
+            sage: isinstance(B.sage()[1], float)  # needs sage.libs.eclib
             True
         """
         E = EllipticCurve(self.ainvs)