CreateGenericValidator: fix reply context fixing

Incoming Pleroma replies to a Misskey thread were rejected due to a
broken context fix, which caused them to not be visible until a
non-Pleroma user interacted with the replies.

This fix properly sets the post-fix object context to its parent Create
activity as well, if it was changed.

lib/pleroma/web/activity_pub/object_validators/create_generic_validator.ex

@@ -75,7 +75,7 @@ defmodule Pleroma.Web.ActivityPub.ObjectValidators.CreateGenericValidator do
 
     data
     |> CommonFixes.fix_actor()
-    |> Map.put_new("context", object["context"])
+    |> Map.put("context", object["context"])
     |> fix_addressing(object)
   end