ConnectionPool: fix the previous hotfix

I rushed the hotfix and forgot how `pop_in` actually works,
I want to die. We need some integration tests for the HTTP client

lib/pleroma/tesla/middleware/connection_pool.ex

@@ -32,7 +32,8 @@ def call(%Tesla.Env{url: url, opts: opts} = env, next, _) do
           {:ok, env} ->
             unless opts[:adapter][:body_as] == :chunks do
               ConnectionPool.release_conn(conn_pid)
-              {:ok, pop_in(env.opts[:adapter][:conn])}
+              {_, res} = pop_in(env.opts[:adapter][:conn])
+              {:ok, res}
             else
               {:ok, env}
             end