Fix type error

Author: araffin

stable_baselines3/her/her_replay_buffer.py

@@ -402,7 +402,7 @@ def truncate_last_trajectory(self) -> None:
                 self.dones[self.pos - 1, env_idx] = True
                 # make sure that last episodes can be sampled and
                 # update next episode start (self._current_ep_start)
-                self._compute_episode_length(env_idx)
+                self._compute_episode_length(int(env_idx))
                 # handle infinite horizon tasks
                 if self.handle_timeout_termination:
                     self.timeouts[self.pos - 1, env_idx] = True  # not an actual timeout, but it allows bootstrapping