code: protected function makeUnique($slug)
      {
          $uniqueSlug = $slug;
          $iteration = 0;
          while (!$this->validateSlug($uniqueSlug)) {
              $iteration++;
              $uniqueSlug = $this->generateUniqueSlug($slug, $iteration);
          }
  
          return $uniqueSlug;
      }
docs: This method is called by [[getValue]] when [[ensureUnique]] is true to generate the unique slug.
  Calls [[generateUniqueSlug]] until generated slug is unique and returns it.
  @param string $slug basic slug value
  @return string unique slug
  @see getValue
  @see generateUniqueSlug
  @since 2.0.7