fix: default value to empty string

Author: guilherme6191

packages/clerk-js/vitest.setup.mts

@@ -103,11 +103,10 @@ if (typeof window !== 'undefined') {
     writable: true,
   });
 
-  // Set default navigator.language to empty to prevent auto-locale injection in tests
   Object.defineProperty(window.navigator, 'language', {
     writable: true,
     configurable: true,
-    value: undefined,
+    value: '',
   });
 
   // Mock IntersectionObserver