Use immutabledict instead of frozendict (#15113)

Additionally:

* Consistently use `freeze()` in test

---------

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>
Co-authored-by: 6543 <6543@obermui.de>

1 files changed, 2 insertions, 2 deletions

diff --git a/synapse/storage/databases/main/stream.py b/synapse/storage/databases/main/stream.py

index ac5fbf6b86..2b8779bbb8 100644
--- a/synapse/storage/databases/main/stream.py
+++ b/synapse/storage/databases/main/stream.py
@@ -50,7 +50,7 @@ from typing import (
 )
 
 import attr
-from frozendict import frozendict
+from immutabledict import immutabledict
 from typing_extensions import Literal
 
 from twisted.internet import defer
@@ -557,7 +557,7 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
                 if p > min_pos
             }
 
-        return RoomStreamToken(None, min_pos, frozendict(positions))
+        return RoomStreamToken(None, min_pos, immutabledict(positions))
 
     async def get_room_events_stream_for_rooms(
         self,