add slnx support #551

Job	Run time
check_code_format	56s
check_licenses_net472 (App)	1m 29s
check_version_command (net6.0)	18s
check_licenses (net6.0, App)	41s
check_version_command (net8.0)	35s
check_licenses (net6.0, Tests)	26s
check_version_command_net472	2m 31s
check_version_command (net9.0)	23s
check_licenses_net472 (Tests)	1m 47s
check_licenses (net6.0, ProjectWithReferenceContainingLicenseExpression)	20s
check_licenses_net472 (ProjectWithReferenceContainingLicenseExpression)	2m 55s
check_licenses (net8.0, App)	45s
test (ubuntu-latest, net6.0)	1m 15s
test_windows (net6.0)	4m 58s
check_licenses (net8.0, Tests)	42s
test (ubuntu-latest, net8.0)	1m 17s
test_windows (net8.0)	4m 27s
check_licenses (net8.0, ProjectWithReferenceContainingLicenseExpression)	18s
test (ubuntu-latest, net9.0)	1m 10s
test_windows (net472)	4m 24s
check_licenses (net9.0, App)	44s
test (macos-latest, net6.0)	1m 9s
test_windows (net9.0)	4m 58s
check_licenses (net9.0, Tests)	32s
test (macos-latest, net8.0)	1m 10s
test (macos-latest, net9.0)	1m 8s
check_licenses (net9.0, ProjectWithReferenceContainingLicenseExpression)	26s
	41m 44s

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