Using better approach for skipping test if Cython no pres.

IPython/extensions/tests/test_cythonmagic.py

@@ -12,8 +12,8 b' code = """def f(x):'
 try:
     import Cython
 except:
-    pass
-else:
+    __test__ = False
+
     def setup():
         ip = get_ipython()
         ip.extension_manager.load_extension('cythonmagic')