Processing chapters does not work.

[thedangler]

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Describe the bug
Chatpers are empty when using yt.chapters.

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code that was used that resulted in the bug

from pytubefix import YouTube
print(yt.chapters)

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Expected behavior

Chapters should be printed out.
When stepping through the code line 534 of main.py is never true because
if marker['key'].upper() == 'DESCRIPTION_CHAPTERS':
is never true.

DESCRIPTION_CHAPTERS key doesn't exist when returning the markers_map.

Two keys were returned 'AUTO_CHAPTERS' and 'ANIMATION_ANNOTATION_MARKERS'

Changing DESCRIPTION_CHAPTERS to AUTO_CHAPTERS worked.

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Desktop (please complete the following information):

• OS: macOS
• Python Version [3.11]
• Pytubefix Version [8.7]

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Additional context
Add any other context about the problem here.

[neurite]

I think we are looking at 2 types of chapters here: one type that are created by the author (as already covered by the original code) and one type that are auto-generated by YouTube (as you are reporting here). The question is whether we treat them the same or we add a 2nd type for auto-chapters. I am leaning toward the latter so that we do not lose the fine-grained differentiation between the 2 types of chapters. If so, this is more like a new feature that may require further discussion.