Gitea repository migration SSRF through DNS rebinding

Gitea validates a repository migration hostname against its network allow and block lists before invoking Git, but the Git subprocess independently resolves the hostname when connecting. An attacker who can start a migration and control the destination's DNS can change the address between validation and connection to reach a blocked internal address. The affected path is the Git clone operation; validation in the migration HTTP client's dialer does not protect the independently connecting Git subprocess.