add support for .net 9 (#110) #542

Job	Run time
check_licenses_net472 (App)	3m 22s
check_code_format	1m 38s
check_version_command (net6.0)	35s
check_licenses (net6.0, App)	39s
check_licenses_net472 (Tests)	3m 29s
check_version_command (net8.0)	22s
check_licenses (net6.0, Tests)	32s
check_licenses_net472 (ProjectWithReferenceContainingLicenseExpression)	3m 15s
check_version_command (net9.0)	29s
check_version_command_net472	1m 59s
check_licenses (net6.0, ProjectWithReferenceContainingLicenseExpression)	45s
check_licenses (net8.0, App)	23s
test (ubuntu-latest, net6.0)	1m 42s
check_licenses (net8.0, Tests)	25s
test_windows (net6.0)	6m 35s
test (ubuntu-latest, net8.0)	1m 20s
check_licenses (net8.0, ProjectWithReferenceContainingLicenseExpression)	19s
test_windows (net8.0)	5m 43s
check_licenses (net9.0, App)	37s
test (ubuntu-latest, net9.0)	1m 23s
test_windows (net472)	3m 9s
check_licenses (net9.0, Tests)	45s
test (macos-latest, net6.0)	1m 41s
test_windows (net9.0)	6m 55s
check_licenses (net9.0, ProjectWithReferenceContainingLicenseExpression)	24s
test (macos-latest, net8.0)	1m 30s
test (macos-latest, net9.0)	1m 44s
	51m 40s

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