deps: Upgrade `freetype-sys` to version 0.21 #212

Job	Run time
stable, Linux, static linking, no pkg-config	1m 27s
stable, Linux, shared library	40s
stable, iOS, static library	38s
stable, macOS, shared library	30s
stable, macOS, static library	40s
stable, Emscripten, static library	1m 22s
stable, Windows, static library	1m 33s
Result	0s
	6m 50s

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