Fix the response format of the /send endpoint

Fixes https://github.com/matrix-org/matrix-doc/issues/2236

api/server-server/transactions.yaml

@@ -77,14 +77,7 @@ paths:
             The result of processing the transaction. The server is to use this response even in
             the event of one or more PDUs failing to be processed.
           schema:
-            type: array
-            minItems: 2
-            maxItems: 2
-            items:
-              - type: integer
-                description: The value ``200``.
-                example: 200
-              - type: object
+            type: object
             title: PDU Processing Results
             description: The results for the processing of each PDU in the transaction.
             properties:
@@ -106,9 +99,7 @@ paths:
                       example: "You are not allowed to send a message to this room."
             required: ['pdus']
           examples:
-            application/json: [
-              200,
-              {
+            application/json: {
               "pdus": {
                 "$successful_event:example.org": {},
                 "$failed_event:example.org": {
@@ -116,4 +107,3 @@ paths:
                 }
               }
             }
-            ]

changelogs/server_server/newsfragments/2560.clarification

@@ -0,0 +1 @@
+Fix the response format of the ``/send`` endpoint.