[utils] Fix race condition in make_dir

[aionescu]

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Call os.makedirs with exist_ok=True, rather than performing a separate check with os.path.exists.

This fixes a race condition that can occur when spawning multiple yt-dlp processes with the same output directory, where one of the processes crashes with Unable to create directory [Errno 17]: File exists, due to the interleaving of calls to os.path.exists and os.makedirs.

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