kdf: Skip tests if hash algo is not available
* tests/t-kdf.c (check_openpgp, check_pbkdf2): Test digest availability.
Skip tests that would fail if libgcrypt is compiled with an
--enable-digests option that does not include the required digest
algorithms for the test vectors.
- GnuPG-bug-id: T6048
- Signed-off-by: Clemens Lang <cllang@redhat.com>