deps: Upgrade `freetype-sys` to version 0.21 #217

Job	Run time
stable, Linux, static linking, no pkg-config	1m 32s
stable, Linux, shared library	26s
stable, iOS, static library	41s
stable, macOS, shared library	31s
stable, macOS, static library	37s
stable, Emscripten, static library	1m 19s
stable, Windows, static library	1m 29s
Result	0s
	6m 35s

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