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Update Microsoft.SourceLink.GitHub requirement from 1.1.* to 8.0.* #29

Job	Run time
build-and-test (ubuntu-latest)	20s
cleanup-code (ubuntu-latest)	1m 28s
inspect-code (ubuntu-latest)	1m 52s
build-and-test (windows-latest)	55s
cleanup-code (windows-latest)	6m 29s
build-and-test (macos-latest)	3m 11s
inspect-code (windows-latest)	6m 58s
cleanup-code (macos-latest)	2m 38s
inspect-code (macos-latest)	4m 31s
publish	0s
	28m 22s

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