Bump threadgate limits (#4268)

Bump threadgate max hidden replies to 300

Author: estrattonbailey

.changeset/lucky-chefs-work.md

@@ -0,0 +1,5 @@
+---
+"@atproto/api": patch
+---
+
+Bump threadgate `hiddenReplies` field `maxLength` to 300.

lexicons/app/bsky/feed/threadgate.json

@@ -32,7 +32,7 @@
           "createdAt": { "type": "string", "format": "datetime" },
           "hiddenReplies": {
             "type": "array",
-            "maxLength": 50,
+            "maxLength": 300,
             "items": {
               "type": "string",
               "format": "at-uri"