Fix /sync example (#2077)

* Fix sync example

The same event should not appear in `state` and in the `timeline` so we cannot use the same event twice.

To provide a `state` example we assume that with lazy-loading the user did not get the state event for `@example:example.org`, so we add one since they sent a message in the timeline.

The events that are referenced include a `room_id`, which doesn't appear on this endpoint, so we copy them without it.

Finally, the `join` event of `@alice:example.org` is wrong because the sender does not match the state key, which wouldn't pass the authorization rules.

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

* Fix the `m.room.member.yaml` example

This is a `join` event, and the `sender` doesn't match the `state_key`, so the event couldn't pass the authorization rules.

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

* Add changelog

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

---------

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

data/event-schemas/examples/m.room.member.yaml

@@ -1,6 +1,7 @@
 {
   "$ref": "core/state_event.json",
   "state_key": "@alice:example.org",
+  "sender": "@alice:example.org",
   "type": "m.room.member",
   "content": {
     "membership": "join",