Cosine Decay Not Properly Enforced

When passing the following hyper-parameters , one expects to see a cosine decay profile:

```
scheduler:
start_weight_decay: ${policy.megatron_cfg.optimizer.weight_decay}
end_weight_decay: ${policy.megatron_cfg.optimizer.weight_decay}
weight_decay_incr_style: "cosine"
lr_decay_style: "cosine"
lr_warmup_iters: 25
lr_warmup_init: 1e-7
```

However, although warmup is properly enforced, learning rate seems to remain constant. Please see the figure below.

We appreciate if there is a solution for actual enforcement of a cosine decay profile.