Add action_repeat argument to SB3 example script

[Ivan-267]

Adds the action repeat option to the SB3 training example:

parser.add_argument(
    "--action_repeat",
    default=None,
    type=int,
    help="Similar concept to frame skip, sends action/gets obs every n frames only. Uses sync node setting if not set here.",
)

Useful for more quickly comparing different action repeat settings without changing it in Godot, but that option remains.
This argument already exists in the Python Godot env, this PR just adds it to the SB3 script.

[Ivan-267]

Server has updated the style tool. I fixed the style errors, this should be ready to merge now.

[Ivan-267]

@edbeeching Can we merge this one?