[ie/Dropbox] Fix extractor

[nathantouze]

Since dropbox updated their share links around July this year, I had to make an update it to keep using this extractor.

This new regex handles old and new link formats.

Dropbox changed their link format earlier this year. The exctractor weren't working anymore with new links. A change was mandatory to keep using the software.
Old formats:

• https://www.dropbox.com/s/<id>/*
• https://www.dropbox.com/sh/<id>/*

Added formats:

• https://www.dropbox.com/e/scl/fi/<id>/*
• https://www.dropbox.com/scl/fi/<id>/*

(EDIT: Also fixed extraction --@bashonly)

Closes #7005, Closes #7696

Template

Before submitting a pull request make sure you have:

• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests
• Checked the code with flake8 and ran relevant tests

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

• I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence) @denhotte and @bashonly are responsible for changes to format extraction code ([Dropbox] Unable to extract mountComponent #7005 (comment))

What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)

Copilot Summary

🤖 Generated by Copilot at e43c809

Summary

📁🔗🎥

Improve Dropbox extractor to support more link formats. Update _VALID_URL in yt_dlp/extractor/dropbox.py to match them.

Dropbox links vary
_VALID_URL adapts
Winter of patterns

Walkthrough

• Expand the _VALID_URL regex pattern to support more Dropbox link formats (link)

[bashonly]

Add a test for each of the new URL formats

[DoubiTe]

@bashonly & @nathantouze this PR is partially fix the extractor because it still generate an error "mountComponent" #7005
Is it possible to fix-it @pukkandan ? Thanks a lot

[bashonly]

Extraction should be working now, you should be able to add/update tests