fix node to object mapping in FGARetriever

[deepu105]

Description

This pull request makes a small fix to the FGARetriever.py file. It corrects the way nodes are mapped and checked for permissions by using the node's id_ attribute as the key, ensuring that permission checks work as intended.

• Bug fix: Node mapping and permission checks
  • Changed the mapping in node_to_obj and the filtering logic to use node.id_ instead of the node object itself as the key, ensuring correct permission lookups. [1] [2]

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not the default branch