Minor: Update parameter type to callable for column filters in SortableTable::set_column_filter

Author: AngelFQC

public/main/inc/lib/sortable_table.class.php

@@ -978,9 +978,9 @@ public function get_sortable_table_param_string()
      * Add a filter to a column. If another filter was already defined for the
      * given column, it will be overwritten.
      *
-     * @param int    $column   The number of the column
-     * @param string $function The name of the filter-function. This should be a
-     *                         function wich requires 1 parameter and returns the filtered value.
+     * @param int    $column     The number of the column
+     * @param callable $function The name of the filter-function. This should be a
+     *                           function wich requires 1 parameter and returns the filtered value.
      */
     public function set_column_filter($column, $function)
     {