fix: PHPDoc block in Translatable facade

Fix fallback method definition that is lacking "void", occasioning code analyzers like PHPStan to fail.

src/Facades/Translatable.php

@@ -7,7 +7,7 @@
 /**
  * @see \Spatie\Translatable\Translatable
  *
- * @method static fallback(?string $fallbackLocale = null, ?bool $fallbackAny = false, $missingKeyCallback = null)
+ * @method static void fallback(?string $fallbackLocale = null, ?bool $fallbackAny = false, $missingKeyCallback = null)
  */
 class Translatable extends Facade
 {