Fix race condition that can be triggered if the token expires right after we...

Fix race condition that can be triggered if the token expires right after we retrieve it, but before we can set the new expiry time.

lib/gitlab/lfs_token.rb

@@ -20,13 +20,8 @@ module Gitlab
     def token
       Gitlab::Redis.with do |redis|
         token = redis.get(redis_key)
-
-        if token
-          redis.expire(redis_key, EXPIRY_TIME)
-        else
-          token = Devise.friendly_token(TOKEN_LENGTH)
-          redis.set(redis_key, token, ex: EXPIRY_TIME)
-        end
+        token ||= Devise.friendly_token(TOKEN_LENGTH)
+        redis.set(redis_key, token, ex: EXPIRY_TIME)
         token
       end