phpstan: remove explicit type hint of union return type

Author: datengraben

src/Service/iCalendar.php

@@ -260,7 +260,7 @@ public function addEvent(
 		string $eventTitle,
 		string $eventDescription,
 		bool $isTimeSpan = false
-	): Event {
+	) {
 
 		if ( is_array( $eventDate ) ) {
 			if ( count( $eventDate ) < 2 || ! ( $eventDate[0] instanceof DateTimeImmutable ) || ! ( $eventDate[1] instanceof DateTimeImmutable ) || $eventDate[0] > $eventDate[1] ) {