Ensure we store pusher data as text (#9117)

I don't think there's any need to use canonicaljson here.

Fixes: #4475.

changelog.d/9117.bugfix

@@ -0,0 +1 @@
+Fix corruption of `pushers` data when a postgres bouncer is used.

synapse/storage/databases/main/pusher.py

@@ -17,14 +17,13 @@
 import logging
 from typing import TYPE_CHECKING, Any, Dict, Iterable, Iterator, List, Optional, Tuple
 
-from canonicaljson import encode_canonical_json
-
 from synapse.push import PusherConfig, ThrottleParams
 from synapse.storage._base import SQLBaseStore, db_to_json
 from synapse.storage.database import DatabasePool
 from synapse.storage.types import Connection
 from synapse.storage.util.id_generators import StreamIdGenerator
 from synapse.types import JsonDict
+from synapse.util import json_encoder
 from synapse.util.caches.descriptors import cached, cachedList
 
 if TYPE_CHECKING:
@@ -315,7 +314,7 @@ async def add_pusher(
                     "device_display_name": device_display_name,
                     "ts": pushkey_ts,
                     "lang": lang,
-                    "data": bytearray(encode_canonical_json(data)),
+                    "data": json_encoder.encode(data),
                     "last_stream_ordering": last_stream_ordering,
                     "profile_tag": profile_tag,
                     "id": stream_id,