Tests: Mark printf wrappers with G_GNUC_PRINTF
Tests: Mark printf wrappers with G_GNUC_PRINTF

If we tell clang that we're passing the arguments on to a compatible
printf call, it can see that we're doing it right, and won't warn us
about -Wformat-nonliteral. This follows up from commit abac67c0.

Signed-off-by: Simon McVittie <0e1aea601907c1a85c2dc96e5ea37e23c58d2e9b@collabora.com>

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib