Support m3u8 ending in playlist plugin

[JOJ0]

Description

m3u8 files are technically supported in the playlist plugin, only the difference in the file ending prevented usage of such files.

• Documentation. (not required, the current wording implies support of m3u files in general, this should include m3u8 which only makes clear that they are UTF-8 encoded)
• Changelog. (will do after review)
• Tests. (not required)

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[Copilot]

Pull Request Overview

This pull request updates the playlist plugin to support m3u8 files by replacing the hardcoded glob pattern with a new constant (M3U_GLOB) used in both playlist scanning and directory listing.

• Introduces the M3U_GLOB constant to capture m3u8 file endings.
• Refactors the file matching checks to use the new constant.

[Copilot]

The glob pattern defined in M3U_GLOB may not match plain '.m3u' files since '?' in fnmatch requires a character. Consider updating the logic to explicitly accept both '.m3u' and '.m3u8' extensions, for example by checking file extensions directly or using multiple patterns.

Suggested change

	M3U_GLOB = "*.[mM]3[uU]8?"
	M3U_GLOB = ('.m3u', '.m3u8')