Use new error codes from latest MSC4306 draft

Author: reivilibre

synapse/api/errors.py

@@ -141,8 +141,10 @@ class Codes(str, Enum):
     INVITE_BLOCKED = "ORG.MATRIX.MSC4155.M_INVITE_BLOCKED"
 
     # Part of MSC4306: Thread Subscriptions
-    SKIPPED = "M_SKIPPED"
-    NOT_IN_THREAD = "M_NOT_IN_THREAD"
+    MSC4306_CONFLICTING_UNSUBSCRIPTION = (
+        "IO.ELEMENT.MSC4306.M_CONFLICTING_UNSUBSCRIPTION"
+    )
+    MSC4306_NOT_IN_THREAD = "IO.ELEMENT.MSC4306.M_NOT_IN_THREAD"
 
 
 class CodeMessageException(RuntimeError):

synapse/handlers/thread_subscriptions.py

@@ -111,7 +111,7 @@ async def subscribe_user_to_thread(
                 raise SynapseError(
                     HTTPStatus.BAD_REQUEST,
                     "Automatic subscription must be caused by an event in the thread",
-                    errcode=Codes.NOT_IN_THREAD,
+                    errcode=Codes.MSC4306_NOT_IN_THREAD,
                 )
 
             stream_ordering = event.internal_metadata.stream_ordering
@@ -135,7 +135,7 @@ async def subscribe_user_to_thread(
             raise SynapseError(
                 HTTPStatus.CONFLICT,
                 "Automatic subscription obsoleted by an unsubscription request.",
-                errcode=Codes.SKIPPED,
+                errcode=Codes.MSC4306_CONFLICTING_UNSUBSCRIPTION,
             )
 
         return outcome