Fix labeling detection bug (#85429)
Fixes a bug where if a PR is pre-labeled with both a `release notes:` label and a `topic:` label then our bot still pings on the PR, erroneously asking for those labels to be added
&-ing sets computes the set intersection, which isn't what was desired here
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85429
Approved by: https://github.com/janeyx99
