GHSA-268j-37xf-pp52: Gogs's write-level collaborators can mutate admin-only repository settings via API

Gogs (a self-hosted Git service) has three API endpoints that incorrectly allow write-level collaborators to change admin-only repository settings. These endpoints use `reqRepoWriter()` middleware instead of `reqRepoAdmin()`, meaning users with basic write access can disable the issue tracker or wiki, inject malicious external URLs that redirect visitors, or trigger mirror sync operations. The web interface correctly requires admin access for these same operations, creating a security inconsistency.