Typehint mutator profile_photo_url attribute function return (#1396)

We need to typehint mutator function return to let IDE Helper package know the type of the attribute.

barryvdh/laravel-ide-helper#1315 (comment)

Then PHPStan will not throw error on undefined profile_photo_url property.

Author: potsky

src/HasProfilePhoto.php

@@ -59,7 +59,7 @@ public function deleteProfilePhoto()
      */
     public function profilePhotoUrl(): Attribute
     {
-        return Attribute::get(function () {
+        return Attribute::get(function (): string {
             return $this->profile_photo_path
                     ? Storage::disk($this->profilePhotoDisk())->url($this->profile_photo_path)
                     : $this->defaultProfilePhotoUrl();