tests,json: Fix match if the first child differs
tests,json: Fix match if the first child differs

* tests/json/t-json.c (test_contains): Try all siblings of
the haystack child.

--
This fixes the case where we don't match against the
first child because the order might have changed or
a new element was inserted at the top. Then we
have to try out also all the siblings.

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme