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/rest/client/v1/utils.py

@@ -132,7 +132,7 @@ class RestHelper:
         src: str,
         targ: str,
         membership: str,
-        extra_data: dict = {},
+        extra_data: Optional[dict] = None,
         tok: Optional[str] = None,
         expect_code: int = 200,
     ) -> None:
@@ -156,7 +156,7 @@ class RestHelper:
             path = path + "?access_token=%s" % tok
 
         data = {"membership": membership}
-        data.update(extra_data)
+        data.update(extra_data or {})
 
         channel = make_request(
             self.hs.get_reactor(),
@@ -187,7 +187,13 @@ class RestHelper:
         )
 
     def send_event(
-        self, room_id, type, content={}, txn_id=None, tok=None, expect_code=200
+        self,
+        room_id,
+        type,
+        content: Optional[dict] = None,
+        txn_id=None,
+        tok=None,
+        expect_code=200,
     ):
         if txn_id is None:
             txn_id = "m%s" % (str(time.time()))
@@ -201,7 +207,7 @@ class RestHelper:
             self.site,
             "PUT",
             path,
-            json.dumps(content).encode("utf8"),
+            json.dumps(content or {}).encode("utf8"),
         )
 
         assert (