deps: Upgrade `freetype-sys` to version 0.21 #218

Job	Run time
stable, Linux, static linking, no pkg-config	1m 25s
stable, Linux, shared library	49s
stable, iOS, static library	44s
stable, macOS, static library	40s
stable, Emscripten, static library	1m 22s
stable, macOS, shared library	29s
stable, Windows, static library	1m 33s
Result	0s
	7m 2s

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