change the return type for LineNumber from int to string

Author: Bertware

src/Trafiklab/Common/Model/Contract/TimeTableEntry.php

@@ -39,9 +39,9 @@ public function getLineName(): string;
     /**
      * The number of the line on which the vehicle is driving.
      *
-     * @return int
+     * @return string
      */
-    public function getLineNumber(): int;
+    public function getLineNumber(): string;
 
     /**
      * The operator of the vehicle.