Add test for lambda inside generator

tests/run/generators.pyx

@@ -307,3 +307,11 @@ def test_nested_gen(int n):
     """
     for a in range(n):
         yield (b for b in range(a))
+
+def test_lambda(n):
+    """
+    >>> [i() for i in test_lambda(3)]
+    [0, 1, 2]
+    """
+    for i in range(n):
+        yield lambda : i