Make phpunit8 compatible

apps/admin_audit/tests/Actions/SecurityTest.php

apps/comments/tests/Unit/Activity/ListenerTest.php

apps/comments/tests/Unit/AppInfo/ApplicationTest.php

...omments/tests/Unit/Collaboration/CommentersSorterTest.php

apps/comments/tests/Unit/Controller/NotificationsTest.php

apps/comments/tests/Unit/EventHandlerTest.php

apps/comments/tests/Unit/JSSettingsHelperTest.php

apps/comments/tests/Unit/Notification/ListenerTest.php

apps/comments/tests/Unit/Notification/NotifierTest.php

apps/dav/tests/unit/Avatars/AvatarHomeTest.php

...ests/unit/BackgroundJob/CleanupInvitationTokenJobTest.php

apps/dav/tests/unit/BackgroundJob/EventReminderJobTest.php

...ckgroundJob/GenerateBirthdayCalendarBackgroundJobTest.php

apps/dav/tests/unit/BackgroundJob/RefreshWebcalJobTest.php

...BackgroundJob/RegisterRegenerateBirthdayCalendarsTest.php

...oundJob/UpdateCalendarResourcesRoomsBackgroundJobTest.php

apps/dav/tests/unit/CalDAV/AbstractCalDavBackend.php

apps/dav/tests/unit/CalDAV/Activity/BackendTest.php

apps/dav/tests/unit/CalDAV/Activity/Filter/CalendarTest.php

apps/dav/tests/unit/CalDAV/Activity/Filter/TodoTest.php