tests:w32: Fix the add-recipeint test for Windows.
* tests/openpgp/add-recipient.scm (add-recipient): Use temporary file REFERENCE, instead of hard-coded "reference". (change-recipient): Likewise.
- Fixes-commit: fde7315e33e797443f8bdb2b5d103a952cceb5fc
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>