deps.ffmpeg, deps.windows: Update libdatachannel to v0.20.1 #240

Job	Run time
Run Pre-Checks	2s
Build FFmpeg (macos-arm64)	30m 9s
Build FFmpeg (macos-x86_64)	27m 17s
Build FFmpeg (linux-x86_64)	14m 53s
Build FFmpeg (windows-x64)	36m 27s
Build FFmpeg (windows-x86)	19m 12s
Build Qt6 (macOS)	7m 52s
Build macOS Dependencies (macos-arm64)	5m 10s
Build Qt6 (Windows) (x64, RelWithDebInfo)	2m 1s
Build macOS Dependencies (macos-x86_64)	5m 36s
Build Windows Dependencies (x64)	13m 33s
Build Qt6 (Windows) (x64, Debug)	2m 14s
Build Windows Dependencies (x86)	12m 3s
Build Qt6 (Windows) (x86, RelWithDebInfo)	1m 46s
Build Qt6 (Windows) (x86, Debug)	1m 51s
Package Windows Qt6 (x64)	12s
Package Windows Qt6 (x86)	12s
Build macOS Dependencies (Universal)	5s
Create macOS Qt6 (macos-arm64)	6s
Create macOS Qt6 (macos-x86_64)	6s
Build FFmpeg (Universal)	8s
Create and upload release	0s
	3h 0m 55s

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