fix: correctly detect old-style MOV files (no ftyp box)

[bajankristof]

No description provided.

[Copilot]

Pull request overview

This PR updates FFMPEG::Media#extname to better handle QuickTime/MOV files where ffprobe can’t determine a major_brand (e.g., old-style MOVs without an ftyp box), and ships the fix as a patch release.

Changes:

• Treat major_brand == nil as a QuickTime MOV for mov|mp4 demuxed formats.
• Add an RSpec example for the “old-style MOV without ftyp” scenario (via stubbing).
• Bump gem version to 8.4.2 and document the fix in the changelog.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
lib/ffmpeg/media.rb	Adjusts extname MOV/MP4 branching to return .mov when major_brand is nil.
spec/ffmpeg/media_spec.rb	Adds a spec asserting .mov when major_brand is nil for a MOV fixture.
lib/ffmpeg/version.rb	Version bump to 8.4.2.
CHANGELOG	Adds release notes for 8.4.2.

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