Move on-issue-labeled to use actions/github-script@v6 (#35474)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/35474

This cleans up our `on-issue-labeled` workflow and makes sure we use only github-scripts. So we don't need to checkout the code & run an external action.

Changelog:
[Internal] [Changed] - Move on-issue-labeled to use actions/github-script@v6

Reviewed By: cipolleschi

Differential Revision: D41522650

fbshipit-source-id: c93d10eddf5be2ca9f779389e8059633291c0138