Now that we don't have any distro stuck with glib-2.56.0, we can
bump the glib version. In fact, this is needed, because of
g_clear_pointer. Since v7.4.0-rc1~301 we declare at compile time
what version of glib APIs we want to use (by setting
GLIB_VERSION_MIN_REQUIRED = GLIB_VERSION_MAX_ALLOWED = 2.56.0),
regardless of actual glib version in the host.

And since we currently require glib-2.56.0 and force glib to use
APIs of that version, some newer bits are slipping from us. For
instance: regular function version of g_clear_pointer() is used
instead of a fancy macro. So what? Well, g_clear_pointer()
function typecasts passed free function to void (*)(void *) and
then calls it. Well, this triggers UBSAN, understandably. But
with glib-2.58.0 the g_clear_pointer() becomes a macro which
calls the free function directly, with no typecasting and thus no
undefined behavior.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.c...>