Move ban invalidation to `User#unban` method

app/models/user.rb

@@ -234,7 +234,10 @@ class User < ApplicationRecord
   end
 
   def unban
-    UseCase::User::Unban.call(id)
+    UserBan.current.where(user_id: self.id).update_all(
+      # -1s to account for flakyness with timings in tests
+      expires_at: DateTime.now - 1.second
+    )
   end
 
   # Bans a user.

lib/use_case/user/unban.rb

@@ -8,10 +8,11 @@ module UseCase
       param :target_user_id, type: Types::Coercible::Integer
 
       def call
-        UserBan.current.where(user_id: target_user_id).update_all(
-          # -1s to account for flakyness with timings in tests
-          expires_at: DateTime.now - 1.second
-        )
+        target_user.unban
+      end
+
+      def target_user
+        @target_user ||= ::User.find(target_user_id)
       end
     end
   end