tests: Fix url generation mocks and cleanup some phpunit code

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

tests/unit/Db/CardTest.php

@@ -47,7 +47,7 @@ class CardTest extends TestCase {
 		return $card;
 	}
 
-	public function dataDuedate() {
+	public static function dataDuedate() {
 		return [
 			[(new DateTime()), Card::DUEDATE_NOW],
 			[(new DateTime())->sub(new DateInterval('P1D')), Card::DUEDATE_OVERDUE],