gutils test: Don't assume that every Unix OS implements os-release(5)
gutils test: Don't assume that every Unix OS implements os-release(5)

os-release(5) is widely implemented on Linux, but not necessarily
ubiquitous: unusual or minimal Linux distributions might not have it.
It could in principle be implemented by any other Unix OS, but in
practice this has not yet happened.

Closes: https://gitlab.gnome.org/GNOME/glib/issues/1906
Fixes: 349318e8 "gutils: Add g_get_os_info()"
Signed-off-by: Simon McVittie <0e1aea601907c1a85c2dc96e5ea37e23c58d2e9b@collabora.com>

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