deps: Upgrade `freetype-sys` to version 0.21 #211

Job	Run time
stable, macOS, shared library	31s
stable, Linux, static linking, no pkg-config	21s
stable, Linux, shared library	25s
stable, iOS, static library	36s
stable, macOS, static library	29s
stable, Emscripten, static library	1m 13s
stable, Windows, static library	56s
Result	0s
	4m 31s

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