tests: Test gcry_pk_hash_sign w/explicit hash algo

• tests/t-ecdsa.c (one_test_sexp): Re-run signature operation with hash algorithm explicitly specified in data_tmpl as documented in the manpage.

Cherry-picked master commit of:
45a139b166a3fa18eb1eddf7e02b5cdd890a6c37

The code path to decode the explicit hash algorithm specification in
data_tmpl was previously not covered by tests. Verifying with
a data_tmpl that contains the hash algorithm as string currently fails
and should be enabled later. See also https://dev.gnupg.org/T6066.

• Signed-off-by: Clemens Lang <cllang@redhat.com>