Bugbear: Add Mutable Parameter fixes (#9682)

Part of #9366

Adds in fixes for B006 and B008, both relating to mutable parameter lint errors.

Signed-off-by: Jonathan de Jong <jonathan@automatia.nl>

tests/http/federation/test_matrix_federation_agent.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
+from typing import Optional
 
 from mock import Mock
 
@@ -180,7 +181,11 @@ class MatrixFederationAgentTests(unittest.TestCase):
                 _check_logcontext(context)
 
     def _handle_well_known_connection(
-        self, client_factory, expected_sni, content, response_headers={}
+        self,
+        client_factory,
+        expected_sni,
+        content,
+        response_headers: Optional[dict] = None,
     ):
         """Handle an outgoing HTTPs connection: wire it up to a server, check that the
         request is for a .well-known, and send the response.
@@ -202,10 +207,12 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.assertEqual(
             request.requestHeaders.getRawHeaders(b"user-agent"), [b"test-agent"]
         )
-        self._send_well_known_response(request, content, headers=response_headers)
+        self._send_well_known_response(request, content, headers=response_headers or {})
         return well_known_server
 
-    def _send_well_known_response(self, request, content, headers={}):
+    def _send_well_known_response(
+        self, request, content, headers: Optional[dict] = None
+    ):
         """Check that an incoming request looks like a valid .well-known request, and
         send back the response.
         """
@@ -213,7 +220,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.assertEqual(request.path, b"/.well-known/matrix/server")
         self.assertEqual(request.requestHeaders.getRawHeaders(b"host"), [b"testserv"])
         # send back a response
-        for k, v in headers.items():
+        for k, v in (headers or {}).items():
             request.setHeader(k, v)
         request.write(content)
         request.finish()