Fix constants test

Author: evhub

coconut/tests/constants_test.py

@@ -98,8 +98,8 @@ def test_imports(self):
                 or PYPY and new_imp.startswith("tkinter")
                 # don't test trollius on PyPy
                 or PYPY and old_imp == "trollius"
-                # don't test typing_extensions on Python 2
-                or PY2 and old_imp.startswith("typing_extensions")
+                # don't test typing_extensions, async_generator on Python 2
+                or PY2 and old_imp.startswith(("typing_extensions", "async_generator"))
             ):
                 pass
             elif sys.version_info >= ver_cutoff: