Fix DummyRequest so that response is created each time

Due to only creating the DummyRequest once various mutations were
bleeding across various different tests. With hilarious results.

pyramid/tests/test_config/test_views.py

@@ -3852,14 +3852,14 @@ class DummyResponse(object):
 class DummyRequest:
     subpath = ()
     matchdict = None
-    response = DummyResponse()
 
     def __init__(self, environ=None):
         if environ is None:
             environ = {}
         self.environ = environ
         self.params = {}
         self.cookies = {}
+        self.response = DummyResponse()
 
 class DummyContext:
     pass