Add LLVM 12 support

[saschanaz]

12.0 is released but is not in the supported version list:

install-llvm-action/index.ts

Lines 36 to 51 in 7673c1a

	const VERSIONS: Set<string> = getVersions([
	"3.5.0", "3.5.1", "3.5.2",
	"3.6.0", "3.6.1", "3.6.2",
	"3.7.0", "3.7.1",
	"3.8.0", "3.8.1",
	"3.9.0", "3.9.1",
	"4.0.0", "4.0.1",
	"5.0.0", "5.0.1", "5.0.2",
	"6.0.0", "6.0.1",
	"7.0.0", "7.0.1",
	"7.1.0",
	"8.0.0", "8.0.1",
	"9.0.0", "9.0.1",
	"10.0.0", "10.0.1",
	"11.0.0", "11.0.1", "11.1.0",
	]);

[KyleMayes]

Released v1.3.0 which adds support for LLVM 12.