examples: fix supabase example for v15 (#76567)

Author: saltcod

examples/with-supabase/components/tutorial/fetch-data-steps.tsx

@@ -16,7 +16,7 @@ values
 const server = `import { createClient } from '@/utils/supabase/server'
 
 export default async function Page() {
-  const supabase = createClient()
+  const supabase = await createClient()
   const { data: notes } = await supabase.from('notes').select()
 
   return <pre>{JSON.stringify(notes, null, 2)}</pre>