Bump ext/SDL from `e761770` to `a637412` #439

Job	Run time
Bindgen / Bindgen AST (Windows, windows-latest, win)	57s
Bindgen / Bindgen AST (macOS, macos-latest, osx)	17s
Bindgen / Bindgen AST (Linux, ubuntu-latest, linux)	23s
Bindgen / Bindgen AST cross-platform	16s
Bindgen / Bindgen C#	19s
Build	0s
Commit	0s
	2m 12s

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