tests: update test-casefolding.t with recent changes

This is caught by the mac-buildbot. This was not found initially because this
test requires a case insensitive filesystem.

I have edited the test file by hand and I suggest to test this on such a system
before pushing.

Differential Revision: https://phab.mercurial-scm.org/D4430

tests/test-casefolding.t

@@ -52,7 +52,8 b' test changing case of path components'
   $ hg ci -Am addb D/b
   $ hg mv D/b d/b
   D/b: not overwriting - file already committed
-  (hg rename --force to replace the file by recording a rename)
+  ('hg rename --force' to replace the file by recording a rename)
+  [1]
   $ hg mv D/b d/c
   $ hg st
   A D/c