tests: conditionalize narrow-widen error output for Windows

tests/test-narrow-widen-no-ellipsis.t

@@ -365,7 +365,8 b' Widening that fails can be recovered fro'
   $ hg bookmarks
    * bookmark                  11:* (glob)
   $ hg unbundle .hg/strip-backup/*-widen.hg
-  abort: $ENOENT$: .hg/strip-backup/*-widen.hg
+  abort: .hg/strip-backup/*-widen.hg: $ENOTDIR$ (windows !)
+  abort: $ENOENT$: .hg/strip-backup/*-widen.hg (no-windows !)
   [255]
   $ hg log -T "{if(ellipsis, '...')}{rev}: {desc}\n"
   11: local