Fix up some typechecking (#6150)

* type checking fixes

* changelog

synapse/api/errors.py

@@ -17,6 +17,7 @@
 """Contains exceptions and error codes."""
 
 import logging
+from typing import Dict
 
 from six import iteritems
 from six.moves import http_client
@@ -111,7 +112,7 @@ class ProxiedRequestError(SynapseError):
     def __init__(self, code, msg, errcode=Codes.UNKNOWN, additional_fields=None):
         super(ProxiedRequestError, self).__init__(code, msg, errcode)
         if additional_fields is None:
-            self._additional_fields = {}
+            self._additional_fields = {}  # type: Dict
         else:
             self._additional_fields = dict(additional_fields)
 

synapse/api/room_versions.py

@@ -12,6 +12,9 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+
+from typing import Dict
+
 import attr
 
 
@@ -102,4 +105,4 @@ KNOWN_ROOM_VERSIONS = {
         RoomVersions.V4,
         RoomVersions.V5,
     )
-}  # type: dict[str, RoomVersion]
+}  # type: Dict[str, RoomVersion]