deps.ffmpeg, deps.windows: Update libdatachannel to v0.20.1 #280

Job	Run time
Run Pre-Checks	5s
Build FFmpeg for macOS (macos-arm64)	11m 28s
Build macOS Dependencies (macos-arm64)	7m 8s
Build FFmpeg for macOS (macos-x86_64)	15m 38s
Build Qt6 (macOS)	10m 9s
Build macOS Dependencies (macos-x86_64)	6m 16s
Build FFmpeg for Windows (x64)	33m 53s
Build FFmpeg for Windows (x86)	23m 24s
Build Windows Dependencies (x64)	2m 44s
Build Qt6 (Windows) (x64, RelWithDebInfo)	2m 1s
Build Windows Dependencies (x86)	9m 27s
Build Qt6 (Windows) (x64, Debug)	2m 21s
Build Qt6 (Windows) (x86, RelWithDebInfo)	3m 20s
Build Qt6 (Windows) (x86, Debug)	2m 36s
Package Windows Qt6 (x64)	10s
Package Windows Qt6 (x86)	10s
Build FFmpeg (Universal)	6s
Build macOS Dependencies (Universal)	6s
Create macOS Qt6 (macos-arm64)	5s
Create macOS Qt6 (macos-x86_64)	7s
Create and upload release	0s
	2h 11m 14s

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