add missing return type declarations

Author: ThomasMeschke

system/Files/File.php

@@ -216,6 +216,9 @@ public function getDestination(string $destination, string $delimiter = '_', int
         return $destination;
     }
 
+    /**
+     * @return false|int|string
+     */
     protected function getSizeByUnitInternal(int $fileSizeBase, FileSizeUnit $unit, int $precision)
     {
         $exponent = $unit->value;

tests/system/Files/FileTest.php

@@ -172,6 +172,9 @@ public function testGetDestination(): void
         unlink(SYSTEMPATH . 'Common_Copy_5.php');
     }
 
+    /**
+     * @return Array<string, Array<int>>
+     */
     public static function provideGetSizeData()
     {
         return [