t/lib-gpg: include separate public keys in keyring.gpg

t/lib-gpg: include separate public keys in keyring.gpg

Since 1e3eefb (tests: replace binary GPG keyrings with
ASCII-armored keys, 2014-12-12), we import our test GPG keys
from a single file. Each keypair in the import stream
contains both the secret and public keys. However, older
versions of gpg reportedly fail to import the public half of
the key. We can solve this by including duplicates of the
public keys separately. The duplicates are ignored by modern
gpg, and this makes older versions work.

Reported by Tom G. Christensen <tgc@statsbiblioteket.dk> on
gpg 1.2.6 (from RHEL4).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>