feat: minimal changes to display inference in pygame

[jobesu14]

Minimal code change to be able to display the agent running in pygame in inference mode.

Steps to run the example_display_inference.py successfully:

1. Perform standard training using the dreamerv3/train.py script

dreamerv3/train.py --logdir ~/logdir/train_crafter_small_1 --configs crafter small --run.script rain --run.log_every 30 --run.save_every 30

2. Load the checkpoint of the training step from point 1. to display the trained agent

example_display_inference.py --logdir ~/logdir/display_crafter_small_1 --configs crafter small --run.from_checkpoint ~/logdir/train_crafter_small_1/checkpoint.ckpt