Update .NET SDK 9.0 #1351

Job	Run time
compute_package_version	6s
check_documentation	37s
build_and_test (ubuntu-latest, Release, roslyn3.8)	25s
build_and_test (ubuntu-latest, Release, roslyn4.2)	19s
build_and_test (ubuntu-latest, Release, roslyn4.4)	2m 42s
build_and_test (ubuntu-latest, Release, roslyn4.6)	6m 28s
build_and_test (ubuntu-latest, Release, roslyn4.8)	2m 29s
build_and_test (ubuntu-latest, Release, default)	2m 22s
build_and_test (windows-latest, Release, roslyn3.8)	1m 24s
build_and_test (windows-latest, Release, roslyn4.2)	1m 11s
build_and_test (windows-latest, Release, roslyn4.4)	4m 5s
build_and_test (windows-latest, Release, roslyn4.6)	3m 52s
build_and_test (windows-latest, Release, roslyn4.8)	4m 1s
build_and_test (windows-latest, Release, default)	4m 25s
create_nuget	1m 40s
validate_nuget	0s
deploy	0s
create_release	0s
	36m 6s

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