Feedstock write access via recycled GitHub usernames

Improper access control in conda-smithy before 3.61.0 allows remote attackers to obtain feedstock repository write access. The invitation-routing logic binds maintainers to mutable GitHub username strings instead of immutable user IDs, so a recycled username receives invitations intended for the former owner. Exploitation requires a maintainer to relinquish a username, the attacker to register it, and a future repository invitation to target that old name; accepting it grants feedstock write access and permits build-recipe or script tampering.