tests/json: Bravo key does not have secret key material

* tests/json/t-keylist-secret.out.json: indicate correctly that the
"Bravo" test key does not have secret key material.

Some older versions of GnuPG are buggy, and will claim "secret: true"
for this key, even though the keyring in question has no secret key
material for it.

The underlying call to gpg looks something like:

gpg --with-colons --with-secret --list-keys -- \
    alpha@example.net bravo@example.net

You can see the change in field 15 of the "pub" and "sub" output.

• Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
• GnuPG-Bug-Id: T4820