Use the shorter phpunit syntax for mocked return values

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

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

apps/dav/tests/unit/AppInfo/PluginManagerTest.php

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

...ckgroundJob/GenerateBirthdayCalendarBackgroundJobTest.php

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

...BackgroundJob/RegisterRegenerateBirthdayCalendarsTest.php

...oundJob/UpdateCalendarResourcesRoomsBackgroundJobTest.php

...v/tests/unit/CalDAV/BirthdayCalendar/EnablePluginTest.php

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

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

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

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

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

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

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

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

...alDAV/Reminder/NotificationProvider/EmailProviderTest.php

...t/CalDAV/ResourceBooking/AbstractPrincipalBackendTest.php

apps/dav/tests/unit/CalDAV/Schedule/IMipPluginTest.php