build: Conditionally build the GPG-related tests
build: Conditionally build the GPG-related tests

Do not build GPG signing/verification tests if `--without-gpgme`
option is used during configuration.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>

Closes: #1889
Approved by: cgwalters

GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree