Added tests for DeleteMultipleContentConfirmationDialog.cs #1685

Job	Run time
build (AuthoringToolTest)	3m 22s
test-platforms (ubuntu-22.04)	1m 30s
build (BackendAccessTest)	2m 12s
test-platforms (ubuntu-20.04)	1m 24s
build (BusinessLogicTest)	1m 59s
test-platforms (windows-latest)	2m 47s
build (DataAccessTest)	2m 54s
test-platforms (macos-latest)	1m 22s
build (GeneratorTest)	1m 56s
build (IntegrationTest)	3m 45s
build (PresentationTest)	3m 7s
build (SharedTest)	2m 13s
finish	4s
send-summary	4s
	28m 39s

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