Disable mac sign if not on main #326

Job	Run time
lint / build	7s
build_macos / build (single, universal)	6m 33s
build_macos / build (double, .double, universal)	6m 50s
build_linux / build (single, x86_64)	7m 23s
build_android / build (single, arm64)	7m 39s
build_linux / build (double, x86_64)	7m 11s
build_web / build (single, wasm32)	10m 15s
build_android / build (single, arm32)	9m 17s
build_web / build (double, wasm32)	10m 18s
build_android / build (single, x86_64)	8m 1s
build_android / build (single, x86_32)	6m 38s
build_ios / build (single, arm64)	3m 23s
build_ios / build (double, arm64, .double)	5m 42s
build_android / build (double, arm64)	7m 16s
build_android / build (double, arm32)	6m 21s
build_windows / build (single, x86_32, Win32)	11m 50s
build_windows / build (single, x86_64, x64)	11m 27s
build_android / build (double, x86_64)	7m 15s
build_windows / build (double, x86_32, Win32)	12m 0s
build_android / build (double, x86_32)	7m 17s
build_windows / build (double, x86_64, x64)	10m 7s
Create Release	0s
	2h 42m 50s

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