fix(ls): recognize OpenAPI 2.0 root element (#3493)

Refs #3480

Author: char0n

packages/apidom-ls/src/services/validation/linter-functions.ts

@@ -23,10 +23,13 @@ import {
 import { FunctionItem } from '../../apidom-language-types';
 
 const root = (el: Element): Element => {
+  const rootElementTypes = ['swagger', 'openApi3_0', 'openApi3_1', 'asyncApi2'];
   let node = el;
-  while (node.parent && !['openApi3_0', 'openApi3_1', 'asyncApi2'].includes(node.parent.element)) {
+
+  while (node.parent && !rootElementTypes.includes(node.parent.element)) {
     node = node.parent;
   }
+
   return node.parent;
 };