py3: convert filename to bytes in test-hardlinks.t

Windows was complaining about passing str to CreateFileA() in win32.py.

tests/test-hardlinks.t

@@ -3,10 +3,10 b''
   $ cat > nlinks.py <<EOF
   > from __future__ import print_function
   > import sys
-  > from mercurial import util
+  > from mercurial import pycompat, util
   > for f in sorted(sys.stdin.readlines()):
   >     f = f[:-1]
-  >     print(util.nlinks(f), f)
+  >     print(util.nlinks(pycompat.fsencode(f)), f)
   > EOF
 
   $ nlinksdir()