healthcheck: report real amount of memory allocated by beam

as opposed to memory currently in use

lib/pleroma/healthcheck.ex

@@ -29,7 +29,7 @@ defmodule Pleroma.Healthcheck do
   @spec system_info() :: t()
   def system_info do
     %Healthcheck{
-      memory_used: Float.round(:erlang.memory(:total) / 1024 / 1024, 2)
+      memory_used: Float.round(:recon_alloc.memory(:allocated) / 1024 / 1024, 2)
     }
     |> assign_db_info()
     |> assign_job_queue_stats()