Insert async keyword as last modifier (#27491)

src/services/codefixes/convertToAsyncFunction.ts

@@ -68,7 +68,7 @@ namespace ts.codefix {
         }
 
         // add the async keyword
-        changes.insertModifierBefore(sourceFile, SyntaxKind.AsyncKeyword, functionToConvert);
+        changes.insertLastModifierBefore(sourceFile, SyntaxKind.AsyncKeyword, functionToConvert);
 
         function startTransformation(node: CallExpression, nodeToReplace: Node) {
             const newNodes = transformExpression(node, transformer, node);