Drop "volatile" for g_once_init_enter locations
Drop "volatile" for g_once_init_enter locations

This fixes a few (fatal in gcc 11) warnings, breaking the CI.

For the original discussion on why this change is needed, see
https://gitlab.gnome.org/GNOME/glib/-/issues/600

GNOME/libsecret,GNOME/libsecret,GNOME/libsecret,GNOME/libsecret