This PR solves these 2 following problems.

1. Last step skipped

`self.global_steps += 1` before if `self.global_steps >=
self.total_training_steps` makes the last step skipped.

We start from step 1, and we expect `self.total_training_steps` in
total.


https://github.com/volcengine/verl/blob/82b38e25c72e1b6de7d7d2092af6e1ed5dd2a400/verl/trainer/ppo/ray_trainer.py#L999-L1001

   When `self.global_steps == self.total_training_steps-1`:

   * we have only executed `self.total_training_steps-1` steps

   * `self.global_steps` is updated to `self.total_training_steps`
* `self.global_steps >= self.total_training_steps` is satisfied, and the
training ends.

   Therefore, we should put `self.global_steps += 1` at last

2. redundant validation and logging

If `self.total_training_steps % self.config.trainer.test_freq == 0` :

   * `self._validate()` will be executed twice 

1.
https://github.com/volcengine/verl/blob/82b38e25c72e1b6de7d7d2092af6e1ed5dd2a400/verl/trainer/ppo/ray_trainer.py#L984

2.
https://github.com/volcengine/verl/blob/82b38e25c72e1b6de7d7d2092af6e1ed5dd2a400/verl/trainer/ppo/ray_trainer.py#L1005

   * logging will also be executed twice

1.
https://github.com/volcengine/verl/blob/82b38e25c72e1b6de7d7d2092af6e1ed5dd2a400/verl/trainer/ppo/ray_trainer.py#L985
and
https://github.com/volcengine/verl/blob/82b38e25c72e1b6de7d7d2092af6e1ed5dd2a400/verl/trainer/ppo/ray_trainer.py#L997
2.
https://github.com/volcengine/verl/blob/82b38e25c72e1b6de7d7d2092af6e1ed5dd2a400/verl/trainer/ppo/ray_trainer.py#L1007