deps: Upgrade `freetype-sys` to version 0.21 #219

Job	Run time
stable, iOS, static library	40s
stable, Linux, shared library	27s
stable, macOS, shared library	35s
stable, Linux, static linking, no pkg-config	1m 24s
stable, macOS, static library	39s
stable, Emscripten, static library	1m 28s
stable, Windows, static library	1m 22s
Result	0s
	6m 35s

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