Fix InteractsWithContainer::withoutMix (#44822)

* Fix InteractsWithContainer::withoutMix

Original `mix()` returns `HtmlString` instance, fake-mix should return the same in case if a developer uses `toHtml()` explicitly. E.g.:

```php
mix('asset.css')->toHtml()
```

* Update assertion to reflect new withoutMix() behaviour

Author: lptn

src/Illuminate/Foundation/Testing/Concerns/InteractsWithContainer.php

@@ -5,6 +5,7 @@
 use Closure;
 use Illuminate\Foundation\Mix;
 use Illuminate\Foundation\Vite;
+use Illuminate\Support\HtmlString;
 use Mockery;
 
 trait InteractsWithContainer
@@ -186,7 +187,7 @@ protected function withoutMix()
         }
 
         $this->swap(Mix::class, function () {
-            return '';
+            return new HtmlString('');
         });
 
         return $this;

tests/Foundation/Testing/Concerns/InteractsWithContainerTest.php

@@ -49,7 +49,7 @@ public function testWithoutMixBindsEmptyHandlerAndReturnsInstance()
     {
         $instance = $this->withoutMix();
 
-        $this->assertSame('', mix('path/to/asset.png'));
+        $this->assertSame('', (string) mix('path/to/asset.png'));
         $this->assertSame($this, $instance);
     }