Update src/utils/files.ts

Co-authored-by: Nikolay Vitkov <34244704+Lightning00Blade@users.noreply.github.com>

Author: OrKoN

src/utils/files.ts

@@ -25,7 +25,7 @@ export async function saveTemporaryFile(
   }
 }
 
-export function ensureExtension(filepath: string, extension: string): string {
+export function ensureExtension(filepath: string, extension: `.${string)`: string {
   const normalizedExtension = extension.startsWith('.')
     ? extension
     : `.${extension}`;