Secure category names leaked via user activity export in Discourse

Discourse is an open source discussion platform. Versions 2.8.2 and prior in the `stable` branch, 2.9.0.beta3 and prior in the `beta` branch, and 2.9.0.beta3 and prior in the `tests-passed` branch are vulnerable to a data leak. Users can request an export of their own activity. Sometimes, due to category settings, they may have category membership for a secure category. The name of this secure category is shown to the user in the export. The same thing occurs when the user's post has been moved to a secure category. A patch for this issue is available in the `main` branch of Discourse's GitHub repository and is anticipated to be part of future releases.