Micro-tweak to a cast.

* subversion/tests/libsvn_fs_fs/fs-pack-test.c
  (test_info): Don't cast away const.  Both sides of the assignment
    are pointers-to-const.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1471706 13f79535-47bb-0310-9956-ffa450edef68