Bump phpunit and fix CI

Signed-off-by: Julius Härtl <jus@bitgrid.net>

tests/unit/Cron/DeleteCronTest.php

@@ -18,7 +18,7 @@
  *
  *  You should have received a copy of the GNU Affero General Public License
  *  along with this program. If not, see <http://www.gnu.org/licenses/>.
- *  
+ *
  */
 
 namespace OCA\Deck\Cron;
@@ -42,7 +42,7 @@ class DeleteCronTest extends \Test\TestCase {
 	/** @var DeleteCron */
 	protected $deleteCron;
 
-	public function setUp() {
+	public function setUp(): void {
 		parent::setUp();
 		$this->boardMapper = $this->createMock(BoardMapper::class);
 		$this->attachmentService = $this->createMock(AttachmentService::class);
@@ -118,4 +118,4 @@ class DeleteCronTest extends \Test\TestCase {
 			->with($attachment);
 		$this->invokePrivate($this->deleteCron, 'run', [null]);
 	}
-}
+}