deps: Upgrade `freetype-sys` to version 0.21 #220

Job	Run time
stable, Linux, static linking, no pkg-config	1m 42s
stable, iOS, static library	35s
stable, Linux, shared library	40s
stable, macOS, shared library	30s
stable, macOS, static library	38s
stable, Emscripten, static library	1m 30s
stable, Windows, static library	1m 38s
Result	1s
	7m 14s

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