Adds a repository to the selected repositories for a user's codespace secret.
You must authenticate using an access token with the codespace or codespace:secrets scope to use this endpoint. User must have Codespaces access to use this endpoint.
GitHub Apps must have write access to the codespaces_user_secrets user permission and write access to the codespaces_secrets repository permission on the referenced repository to use this endpoint.
Add a selected repository to a user secret