Follow-up to r1637400: Fix concurrent test.

* subversion/tests/libsvn_fs/fs-test.c
  (test_fs_merge): Fix copy-n-pasto repo name.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1637404 13f79535-47bb-0310-9956-ffa450edef68