tests: remove potential mtime ambiguity in a dirstate test

If the test was fast enough, some mtime where not stored. We now wait long
enough to ensure the mtime is no longer ambiguous.

Differential Revision: https://phab.mercurial-scm.org/D11798

tests/test-rebuildstate.t

@@ -79,6 +79,7 b' but in the dirstate'
   $ touch foo bar qux
   $ hg add qux
   $ hg remove bar
+  $ sleep 1 # remove potential ambiguity in mtime
   $ hg status -A
   A qux
   R bar
@@ -106,6 +107,7 b' dirstate'
   $ hg manifest
   bar
   foo
+  $ sleep 1 # remove potential ambiguity in mtime
   $ hg status -A
   A qux
   R bar