fix(playground): reset file input after using it

Author: char0n

experiments/apidom-playground/src/features/app/file-importer/components/FileImporter.jsx

@@ -49,6 +49,8 @@ const FileImporter = () => {
 
     reader.onloadend = onloadend;
     reader.readAsText(file);
+    // eslint-disable-next-line no-param-reassign
+    event.target.value = '';
   };
 
   const handleUrlDialogOpen = () => {