use attr.s for VerifyKeyRequest

because namedtuple is awful

changelog.d/5296.misc

@@ -0,0 +1 @@
+Refactor keyring.VerifyKeyRequest to use attr.s.

synapse/crypto/keyring.py

@@ -15,12 +15,12 @@
 # limitations under the License.
 
 import logging
-from collections import namedtuple
 
 import six
 from six import raise_from
 from six.moves import urllib
 
+import attr
 from signedjson.key import (
     decode_verify_key_bytes,
     encode_verify_key_base64,
@@ -57,15 +57,14 @@ from synapse.util.retryutils import NotRetryingDestination
 logger = logging.getLogger(__name__)
 
 
-VerifyKeyRequest = namedtuple(
+@attr.s(slots=True, cmp=False)
-    "VerifyRequest", ("server_name", "key_ids", "json_object", "deferred")
+class VerifyKeyRequest(object):
-)
     """
     A request for a verify key to verify a JSON object.
 
     Attributes:
         server_name(str): The name of the server to verify against.
-    key_ids(set(str)): The set of key_ids to that could be used to verify the
+        key_ids(set[str]): The set of key_ids to that could be used to verify the
             JSON object
         json_object(dict): The JSON object to verify.
         deferred(Deferred[str, str, nacl.signing.VerifyKey]):
@@ -74,6 +73,11 @@ Attributes:
             logcontext.
     """
 
+    server_name = attr.ib()
+    key_ids = attr.ib()
+    json_object = attr.ib()
+    deferred = attr.ib()
+
 
 class KeyLookupError(ValueError):
     pass