fix: use Object.create(null) for dictionary object in toJson serialization

Agent-Logs-Url: https://github.com/microsoft/rushstack/sessions/bf4dc31b-0da1-4979-b465-0bdff2d00028

Co-authored-by: dmichon-msft <26827560+dmichon-msft@users.noreply.github.com>

Author: Copilot

libraries/lookup-by-path/src/LookupByPath.ts

@@ -633,7 +633,7 @@ export class LookupByPath<TItem extends {}> implements IReadonlyLookupByPath<TIt
       }
 
       if (node.children && node.children.size > 0) {
-        const children: Record<string, ISerializedPathTrieNode> = {};
+        const children: Record<string, ISerializedPathTrieNode> = Object.create(null);
         for (const [segment, child] of node.children) {
           children[segment] = serializeNode(child);
         }