Agaric Capistrano task update error caused by server permissions

The error:

ben@ebony-ubuntu:~/code/mind/drupal/sites/all/modules/imagecache_actions$ cap agaric:update
  * executing `agaric:update'
Everything up-to-date
  * executing "cd /var/www/mind && git pull agaric master"
    servers: ["server.grassrootsconnection.org"]
    [server.grassrootsconnection.org] executing command
*** [err :: server.grassrootsconnection.org] From /srv/git/mind
*** [err :: server.grassrootsconnection.org] * branch            master     -> FETCH_HEAD
** [out :: server.grassrootsconnection.org] Updating 7e99f41..2cbcab5
*** [err :: server.grassrootsconnection.org] error: unable to unlink old 'drupal/sites/all/modules/imagecache_actions/utility.inc' (Permission denied)
*** [err :: server.grassrootsconnection.org] error: git-checkout-index: unable to create file drupal/sites/all/modules/imagecache_actions/utility.inc-491038.patch (Permission denied)
    command finished
failed: "sh -c 'cd /var/www/mind && git pull agaric master'" on server.grassrootsconnection.org

And the fix: