TEST: Fix path length in test/ossl_store_test.c

TEST: Fix path length in test/ossl_store_test.c

The URI length was set to 80 chars, but the URI being built up may
need more space, all depending on the paths used to get to the files
that are to be loaded.  If the result needs more than 80 chars, the
test will fail.

Fixed by using PATH_MAX.

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/13546)