Mark the conversations with the blocked user as read and update the blocking user's unread_conversation_count.

Since the conversations with the blocked user are invisible, they are excluded
from the blocking user's `unread_conversation_count`.

lib/pleroma/web/pleroma_api/controllers/pleroma_api_controller.ex

@@ -80,7 +80,7 @@ defmodule Pleroma.Web.PleromaAPI.PleromaAPIController do
   end
 
   def read_conversations(%{assigns: %{user: user}} = conn, _params) do
-    with {:ok, participations} <- Participation.mark_all_as_read(user) do
+    with {:ok, _, participations} <- Participation.mark_all_as_read(user) do
       conn
       |> add_link_headers(participations)
       |> put_view(ConversationView)